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THE  flANUFACTURE  OF 

CELLULOSE. 


A  Practical  Treatise   for    Paper  and    Cellulose  Tech. 
nologists,  Managers  and  Superintendents, 

BY 

MAX  SCHUBERT, 

Royal  Polytechnical  School,  Dresden. 


Specially  Translated  for  The  American  Paper  Trade. 
107  ILLUSTRATIONS. 


ANDREW  QEYER, 

318  Broadway. 


COPYRIGHTED   1899 

BY 

ANDREW   GEYER. 


GENERAL 


PREFACE. 


*fjgEFORE  complying  with  the  request  of  Herr  Fisher, 
•^  publisher  in  Berlin,  to  compile  for  his  technological 
library,  a  small  work  on  "the  manufacture  of  cellulose/' 
I  have  first  considered  whether  there  existed  a  necessity 
for  such.  Although  several  short  treatises  on  the  com- 
paratively new  industrial  branch,  "the  manufacture  of  cel- 
lulose" have  already  appeared,  the  main  published  infor- 
mation has  been  in  the  several  volumes  of  the  Papier  Zei- 
tung,  and  other  trade  journals  which  contain  a  number  of 
articles  about  special  departments  of  the  industry  and  re- 
lating questions.  The  above  mentioned  compilations  are 
treated  in  a  general  way  and  are  short,  forming  chapters 
of  larger  w^orks  on  the  manufacture  of  paper,  while  the 
different  articles  in  the  papers  are  so  much  distributed 
among  others,  partly  also  connected  with  personal  contro- 
versies and  views,  that  I  have  become  convinced  of  the 
necessity  and  the  meritoriousness  of  the  labor.  To  sift  this 
comparatively  valuable  material,  to  complete  it  with  per- 
sonal experiences,  and  by  adding  practical  advice,  to  create 
an  up  to  date  book  on  the  subject  of  "Cellulose"  seemed  to 
me  eminently  desirable  and  I  therefore  seized  with  eager- 
ness 'the  task  assigned  me.  I  also  communicated  with 
some  men  closely  connected  with  the  manufacture  of  cellu- 
lose, and  to  them  I  am  obliged  for  valuable  details.  I  have 
found,  however,  that  it  is  impossible  to  give  an  entirely 
exhaustive  account  of  this  branch,  because  not  only  are 
the  many  different  systems  in  use  in  the  manufacture  of 
cellulose  patented,  but  almost  every  manufacturer  endeav- 
ors to  invest  his  process  with  all  possible  secrecy.  I  have 
consequently  treated  copiously  but  one  of  the  best  intro- 
duced processes,  and  the  others  I  have  but  touched,  sketch- 
ing in  the  principal  features  of  each. 

In  starting  the  book  I  adopted  the  principle  of  treating 
the  manufacture  in  its  successive  phases,  and  with  each 
chapter  to  consider  the  peculiarities  of  the  different  sys- 
tems one  after  the  other.  In  this  manner  I  have  avoided 
repetitions,  as  some  manipulations  in  the  manufacture  of 
cellulose  are  the  same  in  all  processes,  especially  as  to  the 


102018 


4  PREFACE. 

beginning  with  the  pulp  wood  as  well  as  the  finishing  of 
the  cellulose  for  shipping. 

First  of  all  the  book  treats  of  the  raw  Material,  the 
wood,  with  a  description  of  the  machinery  -oMessary  in  it, 
and  then  passes  over  to  the  preparation  ^  the  leaches. 
Next  the  soda  process  is  treated  in  •  connection,  with  the  re- 
generation of  the  soda  and  thereafter  the  sjflphite  process 
is  considered  in  its  different  variations  a'uSijfatest  improve- 
ments by  text  and  illustration.  The  (Mcription  of  the 
processes  of  boiling  in  the  <liflVn>ii 

consideration  of  the  boilers  as  differing''  in  size,  form, 
material  and  lining,  and  the  methods  for  the  finishing  of 
the  products  follow. 

A  higher  value,  however,  than  on  the  description  of 
manufacture  proper  and  of  the  necessary  apparatus  and 
machines  is  to  be  placed  on  the  open  discussion,  contained 
in  the  last  chapter,  of  the  difficulties,  which  are  encoun- 
tered in  the  manufacture  of  cellulose  in  the  riddance  and 
harmless  disposal  of  the  spent  liquors  and  offensive  gasses. 
The  same  is  true  of  the  practical  advice  which  is  given  in 
regard  to  planning  of  new  factories.  The  liberal  use  of  cel- 
lulose has  already  caused  a  revolution  in  the  extensive  pa- 
per industry,  as  it  is  no  longer  absolutely  necessary  to  look 
for  accommodations  of  large  water  power,  or  to  provide 
extensive  rag  lofts;  because  with  steadily  advancing  im- 
provement in  cellulose  its  use  will  still  grow.  Consequently 
the  circle  of  all  those  who  are  interested  in  learning  the 
particulars  about  the  production  of  cellulose  and  its  prop- 
erties must  expand. 

The  expectation  of  success  of  the  present  book,  as  ex- 
pressed in  the  preface  to  the  first  edition,  has  fortunately 
become  fulfilled  to  me  as  well  as  the  publisher;  for  be- 
sides the  congratulations  sent  me  from  different  sides,, 
shortly  after  the  publication,  a  French  translation  was 
prepared  by  the  well  known  publishers,  Baudry  &  Cie,  in 
.Paris,  edited  by  sub-director  Mons,  B.  Bibas.  Almost,  at 
the  same  time  I  was  negotiating  for  the  preparation  of  a 
Eussian  edition  with  a  Russian  engineer,  but  I  do  not 
know  whether  the  translation  was  executed,  as  on  my  men- 
tioning of  a  trifling  consideration,  the  correspondence 
from  that  side  was  cut  off,  and  Germany  is  not  in  literary 
convention  with  Russia.  Moreover,  the  entire  edition  was 
sold  out  in  two  years,  so  that  many  orders  could  not  be 


PREFACE.  5 

accepted.  Outside  causes  were  responsible  for  the  long  de- 
lay of  the  publication  of  the  completed  edition  of  this 
work. 

During  the  last  four  years,  although  no  new  processes 
appeared  in  the  manufacture  of  cellulose,  a  considerable 
number  of  changes  and  improvements  were  made,  which 
deserved  mention  in  the  new  edition.  Those,  therefore, 
besides  the  personal  practical  experience  recently  obtained 
have  been  incorporated  in  the  new  edition.  I  have  also 
used  all  information  which  was  furnished  to  me  by  the 
several  inventors  of  the  processes  and  the  manufactures  of 
machinery,  and  also,  as  in  the  first  edition,  several  arti- 
cles and  sketches  from  the  last  volumes  of  the  Papier 
Zeitung.  In  the  new  book  the  representation  of  the  cell- 
stuff  manufacture  is  so  supplemented  and  rendered  up  to 
date  and  complete  that  instead  of  fifty-seven  illustrations 
107  figures  are  now  necessary  to  supplement  the  descrip- 
tions. 

I  hope  that  the  second  edition  of  my  work  will  fully 
meet  its  claim  of  offering  in  handy  form  all  the  informa- 
tion that  is  desirable  to  the  technologist. 

Dresden,  September  1896. 

MAX  SCHUBERT. 


Cellulose  or  wood  fibre  is  one  of  the  most  important  and 
most  extensively  diffused  substances  throughout  nature 
produced  during  milenaries  by  the  activity  of  the  plants, 
stored  up,  though  changed  by  terrestrial  revolutions,  in  the 
form  of  coal  and  continuously  renewed  by  the  present 
flora.  Consideration  of  the  immense  variety  of  these  pro- 
ducers explains  why  wood  fibre  in  a  mechanical  and  chem- 
ical sense  also  shows  great  differences,  so.  that  the  name 
wood  fibre  is  really  but  an  appelative,  and  for  proper  de- 
scription the  origin  should  be  affixed  every  time,  as  has  al- 
ready been  proposed  from  different  sides.  As,  however,  in 
practice  but  few  kinds  of  fibre  enter  into  question,  namely, 
wood,  straw  and  esparto,  and  as  this  book  treats  of  the 
most  important  only  which  is  ligneous  fibre,  the  designa- 
tion wood  fibre  will  suffice,  and  when  the  more  frequently 
used  synonymous  expression,  "Cellulose"  is  employed,  it 
should  always  be  understood  as  wood  fibre.  The  expression 
cellulose  has  first  been  used  by  Tessie  du  Motay. 

With  the  exception  of  cotton  the  vegetable  fibre  is  sel- 
dom found  exposed,  but  is  enclosed  by  different  more  or 
less  soluble  incrusting  accessories.  Mechanical  disintegra- 
tion of  the  wood  does  not  separate  them,  although  it  fur- 
nishes as  wood  pulp  a  product,  which  on  account  of  its 
cheapness,  has  been  of  great  use  to  the  paper  industry,  be- 
cause it  has  made  possible  the  production  in  large  quanti- 
ties of  low  grade  printing  paper.  The  short  quality  of 
ground  wood  pulp,  its  stiffness,  poor  felting  capacity  and 
its  resistance  to  bleaching  agents  prevent  it  from  becom- 
ing a  substitute  for  wood  fibre.  Not  until  we  succeeded  in 
freeing  the  wood  fibre  from  its  incrustation  by  chemical 
means,  and  on  a  large  scale  at  low  cost,  did  we  obtain 'a  ma- 
terial ca.pa.ble  of  causing  the  revolution  in  the  paper  in- 
dustry mentioned  in  the  preface.  As  is  the  case  with  all 
important  discoveries,  it  took  considerable  time  before  the 
experiments  in  the  separation  of  vegetable  fibre,  dating 
since  the  year  1840,  led  to  the  practical  results  by  which 
we  have  profited  in  so  great  a  measure.  By  different  ways, 
successively  and  repeatedly  improving  the  method  of  their 


8  THE    MANUFACTURE    OF    CELiLULO&E. 

predecessors,  a  number  of  men  succeeded  in  manufactur- 
ing cellulose,  and.  later  on  several  large  groups  have  be- 
come crystalized  according  to  the  method  of  manufacture. 
The  thickness  of  fibre',  strength,  purity,  elasticity  and 
bleaching  capacity  of  the  different  cellulose  thus  produced 
are  to  the  advantage  of  the  paper  manufacturer,  because 
the  demands  are  endlessly  varying  and  the  manufacturer 
is  in  a  position  to  select  the  different  suitable  sorts  or  to 
work  in  several  at  the  same  time. 

Xotwithstanding  the  different  methods  and  the  differ- 
ence in  the  details  of  the  manufacture  a  conclusion  as  to 
the  best  method  of  development  has  not  yet  been  reached, 
for  very  lately,  electricity  has  entered  the  arena,  to  assist 
in  dissolving  the  incrusting  constituents  of  the  fibre. 

The  evolution  of  the  very  important  invention  of  the 
production  of  cellulose  may  be  best  illustrated  by  the  fol- 
lowing chronological  list  of  the  names  of  those  men  who 
are  either  inventors  of  new  methods  or  who  merit  notice 
by  improvements  and  the  introduction  of  practical  appa- 
ratus, etc. 


Year.  Name. 

1840  Paven. 

1852  Coupler   &   Mellier. 

1853  Watt  &  Burgess. 
1855  Juillon. 

1857  Houghton. 
1861  Barre  &  Blondel. 
1864  Bachet&Machard. 
1866  Tilghmann. 


1866  Ekman. 

1867  Fry. 

1870  Dresel. 

1871  R.    Mitscherlich. 

1872  Unge-rer. 

1872  Ritter-Kellner. 


1873  Roemer     (in 
tingsdorf). 
Orioli. 

1880  Cross. 

1881  Francke. 

1882  Pictet. 

1882  Graham. 

1882  Flodquist. 

1883  Blitz. 

1883  Dahl. 
1885  Kellner. 
1890  Lifschutz. 


Net- 


Dissolving-  Agent. 

Nitric  acid. 

Soda. 

Alkalies. 

Alkal  ne  bases. 

Alkalies. 

Aquous  acids. 

Hydrochloric    acid. 

Sulphite  of  lime  dis- 
solved in  sulphurous 
acid. 

Sulphite   of  magnesia. 

Water  of  high  temper- 
ature. 

Soda. 

Sulphurous   acid. 

Soda. 

Sulphurous  acid. 

Nitric  acid  cold  method. 

Aqua    regia. 

Water  with  neutral  sul- 
phites. 

Sulphurous   acid. 

Aquous  solution  of  sul- 
phur dioxide. 

Sulphurous  acid. 

Sulphurous  acid. 

Alkal' es   and   sulphites. 

(Amonium  Vanadinate). 

Sulphate. 

Electricity. 

Nitre-sulphuric    acid. 


Method. 
Acid  process. 
Soda  process. 
Soda  process. 
Soda  process. 
Soda  process. 
Acid  process. 
Acid  pro-cess. 


Sulphite  process. 


Soda  process. 
Sulphite  process. 
Soda  process. 
Sulphite  process. 
Acid  process. 

Acid  process. 

Sulphite  process. 
Sulphite  process. 

Sulphite  process. 
Sulphite  process. 
Sulphite  process. 

Sulphite  pro-cess. 
Soda  process. 
Electric  process. 
Acid  process. 


THE    MANUFACTURE    OF    CELLULOSE.  9 

There  are  thus  four  processes:  1.  The  acid  process.  2. 
The  soda  process.  3.  The  sulphite  process.  4.  The  elec- 
tric process.  Of  these,  the  first,  the  acid  process  is  no 
longer  of  importance  in  practice;  it  has  now  but  theoretic 
and  historic  value.  Besides  the  above  mentioned,  nitric 
acid,  nitre-muriatic  acid,  muriatic  acid  and  sulphuric  acid 
were  also  used  by  some  for  the  purpose  of  cellulose  man- 
ufacture, but  on  account  of  many  disadvantages  were  dis- 
carded wrhen  the  other  methods  proved  more  practical. 
These  three  other  methods,  viewed  from  a  general  stand- 
point, have  one  point  in  common.  The  cellulose  is  pro- 
duced, by  treating  the  disintegrated  wood  with  a  solution 
under  pressure  in  a  boiler  and  by  washing  and  milling. 
The  details  naturally  vary,  some  manipulations,  however, 
especially  at  the  start  and  finish  are  the  same  with  all 
methods.  In  this  treatise,  which  is  to  serve  in  practice 
first  of  all,  the  methods  shall,  therefore,  not  be  gone  over 
one  by  one,  as  then  much  would  have  to  be  repeated;  but 
the  whole  of  the  cellulose  manufacture  will  be  described 
in  its  successive  phases,  while  the  variations  of  the  differ- 
ent systems  will  be  considered  as  points  of  difference  arise. 

Efforts  have  been  made  to  produce  cellulose  from  every 
kind  of  cheaply  obtainable  wood  species,  leaved  wood  as 
well  as  pine,  but  in  general  the  wood  of  the  pine  and  fir 
have  given  the  longest  and  best  fibre,  though  even  in  pine 
this  varies  according  to  the  location  of  the  tree,  and  its 
quicker  or  slower  growth.  Pine  wood  cells  measure  up  to 
9  mm.  the  longest  way,  while  the  leaved  woods  have  a 
much  shorter  fibre.  The  quality  of  cellulose  yielded  by 
different  woods  may  be  seen  in  the  following  table  by  R.  B. 
Griffin  and  A.  D.  Little. 


2l 


Specie  of  Wood.        5  ~ 


Fir    .................  2.81  2.73  66.32 

Poplar    ..............  4.80  1.85  80.35 

Birch    ................  2.14  0.93  82.99 

Yellow    birch    .  1.88  0.97  82.36 


10 


THE    MANUFACTURE    OP    CELLULOSE. 


In  regard  to  soda-cellulose  the  following  table  is  inter- 
esting. It  gives  the  yield  in  cellulose  from  one  volumeter 
each  of  the  different  kinds  of  wood;  it  also  gives  the  loss 
by  barking  and  cleaning. 


Species  of  Wood 
Recently  Cut. 


bJC 


m   -J 

•3" 


•So 


fisi 


.2  U     .i|  O 


Kilo. 

Pine    617.5 

Spruce    Fir    566 

Scotch    or    White-fir...  697.5 

Black    Fir    707.5 

Larch     597.5 

Leg  Fir,    dwa-rf  pine...  449.3 

Red    Beech    865 

White    Birch     623.5 

Asp    695 

Poplar    650 

Mountain    Ash     725.5 

Wild    Service    Tree 756.5 

Border   Willow    •  572.5 

Brittle    Willow    583.5 

Ash    593.5 

Alder    .  516.5 


- 

Per 

Kilo. 

Kilo. 

Kilo. 

Kilo. 

cent 

80 

230 

307.5 

108.2 

35 

136 

191.7 

238.3 

88.2 

37 

170 

252.2 

275.3 

105.7 

38 

147 

285.6 

274.9 

89 

34 

90 

160.37 

347.13 

116.8 

33 

55.1 

124.8 

269.4 

99.81 

37 

70 

327.54 

467.46 

139.8 

30 

111.5 

215.04 

296.96 

85.6 

29 

135 

227.36 

332.64 

108.42 

32 

175 

226.5 

248.5 

88.14 

35 

131.5 

269.67 

324.33 

100.6 

31 

166.5 

224.2 

365.8 

103.96 

28 

80.5 

241 

251 

85.7 

34 

111 

181.4 

291.1 

104.8 

36 

91 

100.1 

402.4 

103.95 

26 

97.5 

181 

238 

82.3 

34 

The  above  analysis  shows  that  the  yield  in  cellulose,  ex- 
pressed in  percentage,  does  not  vary  much  in  the  different 
kinds  of  wood,  though  in  general  the  pines  give  a  some- 
what larger  amount  of  cellulose.  Besides  this  the  quality 
of  cellulose  from  pinesi  is  better,  and  as  this  wood  is  more 
plentiful,  the  price  is  lower.  As  a  result  these  kinds  are 
principally  used. 

The  Scotch  pine,  though  abundant,  in  some  countries 
and  cheap,  is  on  account  of  its  large  content  of  resin,  sel- 
dom used  for  cellulose,  although  under  certain  conditions 
it  yields  a  good  product  as  Herr  Dresel  in  Dalbke  has 
proved  by  his  method. 

Since  the  manufacture  of  cellulose  and  wood  pulp  has 
reached  such  immense  proportions  speedy  extirpation  of 
our  forests  by  this  industry  and  the  inevitable  conse- 
quences of  irrational  forestry  are  suggested.  Fortunately 


THE    MANUFACTURE    OP    CELLULOSE.  11 

a  satisfactory  answer  to  this  can  be  given  by  the  following 
figures  and  explanations,,  which  are  taken  from  a  lecture 
by  Dr.  Frank  as  published  in  the  Papier  Zeitung: 

"In  Germany  there  at  present  about  sixty  cellulose 
factories,  which  work  into  wood  fibre  stuff  about  2,000 
festmeters,  equal  to  3,000  volumeters  of  wood  per  day, 
thus  turning  over  thirty  millions  of  marks  per  annum,  of 
which  amount  about  ten  millions  will  flow  into  the  treas- 
ury of  the  forest  administration.  This  daily  quantity  of 

3.000  volumeters  requires  the  cutting  of  an  area  of  six  to 
eight  hectars  of  forest.     According  to  information  from 
a  competent  party  in  Germany,  in  sixty  years  rotation  the 
average  yearly  yield, in  -solid  wood  may  be  put  for  fir  at 

3.1  festmeters,  for  pine  4.9  fm.,  so  that  the  yearly  need  of 
our  cellulose  factories  to  the  amount  of  600,000  festmeters 
the  regular  yield  of  a  forest  area,  of  from  150,000  to  160,- 
000  had  is  fully  required.  Pine  being  especially  suitable  for 
wood  fibre  the  prices  of  this  wood,  which  formerly  on  ac- 
count of  its  poor  qualifications  for  timber  were  far  below 
those  of  fir,  have  rapidly  risen  and  the  far-seeing  Prussian 
forest  administration  has  already  by  increased  cultivation 
so  well  met  this  condition  that  at  present  274,416  hectar 
o<f  pine  forest  in  the  possession  of  the  State  contain  8,308 
hectar  of   100-year   stock,    17,727   hectar   of   81-100-year 
stock,  30,752  hectar  of  61-80-year  stock,  48,413  hectar  of 
41-60-year  stock,  65,616  hectar  of  21-40-year  stock,  92,675 
hectar  of  1-20-year  stock.     To  this  increased  pine  culture, 
in  which  also  the  forests  in  private  possession  will  follow 
suit,  is  the  more  important;  as  in  the  manufacture  of  wood 
fibre  we  must  reckon  writh  the  competition  of  other  coun- 
tries, which  get  the  wood  material  much  cheaper  than  we 
do;  in   Europe   there  are  especially   Sweden    and    Baltic 
provinces  of  Prussia,  both  very  favorably  situated  coun- 
tries for  export,  and  in  America,  Canada  now  enters  into 
competition  with  equal  facilities. 

A  festmeter  of  pine  wood  weighing  about  450  kilos, 
above  7  festmeter  correspond  to  about  3,150  kilos  of  pure 
wood  pulp  and  as  6  festmeters  pine  wood  yield  about  1,000 
kilos  of  pure  wood  fibre,  the  annual  yield  per  year  of  the 
pine  would  correspond  to  1,166  kilos  of  cellulose  pro- 
duced thereof  per  hectar. 

Each  individual  cellulose  concern  must  procure  the  most 
suitable  pulp  wood  at  the  lowest  shipping  expense.  In 


12  THE    MANUFACTURE    OF    CELLULOSE. 

this  connection  it  is  to  be  considered  that  freshly  cut 
wood  is  the  easiest  worked,  and  produces  the  best  cellu- 
lose, but  it  weighs  heavier  and  by  increase  of  freight  be- 
comes dearer.  It  is  therefore  to  be  recommended  that 
when  the  logs  first  enter  the  factory  they  be  assorted,  sep- 
arating the  older  and  dryer  ones.  Of  the  dry,  which  were 
lying  in  the  woods  a  considerable  time,  special  care  is  to 
be  taken  to  throw  out  those  rotten  in  the  core,  because 
such  partially  reddened  wood  produces  but  inferior  cellu- 
lose. In  any  case,  when  cutting  the  logs  later  on,  the  various 
pieces,  exhibiting  a  change  in  the  white  wood  color,  should 
be  laid  aside,  to  be  used  as  kindling  wood,  or  when  enough 
has  accumulated  to  be  worked  into  third  quality  cellulose. 

WOOD  WORKING. 

The  wood  used  in  cellulose  manufacture  must  first  be 
barked,  and  such  is  done  either  by  hand,  with  the  knife,  or 
by  a  barking  machine,  also  by  both  methods  successively. 

When  heavier  wood  has  to  be  worked,  and  when  the 
barking  is  to  be  done  by  machine,  it  becomes  necessary  to 
cut  the  logs  with  a  log  saw,  swinging  like  a  pendulum,  in- 
to pieces  of  about  60  cm.  long.  In  figures  1  and  2  such 
practical  sa,w  is  illustrated.  A  wooden  frame,  the  length 
of  which  depend  on  the  height  of  the  workshop,  is  on  its 
upper  end  provided  with  two  wooden  pins,  resting  in  two 
hanger  boxes  BB.  In  the  lower  end  of  the  swinging 
frame  is  rested  a  short  shaft,  to  which  on  the  left  is  fast- 
ened the  circular  saw-blade  of  860  mm.  diameter,  which  by 
transmission  receives  a  velocity  of  about  900  revolutions 
per  minute.  In  front  and  at  the  side  of  the  circular  saw 
is  placed  a  wooden  frame,  provided  with  sliding  rollers,  up- 
on which  the  log  is  laid  and  easily  pushed  against  the  saw- 
blade. 

With  his  right  hand  the  operative  presses  the  toothed 
lever  against  the  log,  to  hold  it  in  position  and  with  the 
left  hand  with  one  grasp  he  pulls  the  rotating  saw  against 
the  log,  cutting  through  it  rapidly.  Its  own  weight  at 
once  brings  the  frame  back  to  the  vertical  position,  the 
helper  again  pushes  the  log  ahead  and  the  cutting  is  re- 
peated. In  this  operation  it  can  be  easily  noticed  on  the 
cut  edges,  whether  the  wood  is  part  good  or  part  rotten, 
and  the  bad  pieces  are  thrown  out,  as  stated  above.  With 
great  rapidity  now  follows  the  use  of  the  barking  ma- 


THE    MANUFACTURE    OF    CELLULOSE. 


13 


chine,  of  which  figures  3,  4  and  5  show  a  practical  con- 
struction. 

Encased  in  a  cast  iron  frame  the  barking  machine  is 


BLOCK  SAW. 


set  upon  a  vertical  shaft,  the  principal  part.,  a  circular  ta- 
ble or  wheel  of  830  mm.  diameter,  revolving  330  times 
per  minute.  This  wheel  has  near  the  periphery  five  slits, 


14 


THE    MANUFACTURE    OP    CELLULOSE. 


as  shown  in  figure  4,  through  which  from  below,  diagon- 
ally movable  knives  are  put,  which  are  raised  above  £he 
table  but  a  few  mm.,  and  while  rapidly  revolving  peel  off 


v~rr 

n 


f=\ 


BARKING  MACHINE. 

in  long  slices  the  bark  off  the  wooden  block  c,  which  is 
pressed  against  the  knives  by  the  lever  9.  As  the  block  is 


THE    MANUFACTURE    OF    CELLULOSE.  15 

also  kept  turning  by  a  toothed  wheel,  the  barking  is  done 
equally  over  the  whole  circumference.  If  now  all  blocks 
were  exactly  cylindrical,  the  work  in  the  manner  described 
would  suffice,  but  some  pieces  are  crooked  and  often  have 
humps  and  hollows,  and  it  is  also  necessary  that  not  only 
the  brown  bark,  but  also  the  underlying  white  bast  be  re- 
moved in  order  to  produce  a  good  cellulose.  Consequently 
after  cleaning  with  the  axe  or  knife  on  the  ordinary  work 
bench  must  follow.  Exact  experiment  by  the  author  with 
wood  of  estimated  weight  and  nearly  equal  bulk  have 
shown  the  following  results.  When  the  wood  is  barked  by 
machine  and  after  cleaning  by  hand,  10  festmeters  cost 
about  5.5  marks  for  labor,  while  10  marks  have  to  be  ex- 


FIG.  5.     BARKING  MACHINE. 

pended  when  barked  by  hand  only.  In  the  latter  case  it 
is  true  the  loss  by  barking  is  about  1.4  per  cent  less,  never- 
theless the  use  of  the  machine  is  to  be  recommended,  as 
thus  much  time  and  money  are  saved. 

In  place  of  the  above  described  barking-machine  a  so- 
called  duplex  may  be  used,  on  which  two  blocks  can  be 
worked  at  the  same  time,  or  also  one  with  a  wheel  rotating 
vertically.  The  barking  shop  is  generally  located  on  the 
ground  floor  of  the  factory.  By  an  elevator  the  barked 


16 


THE    MANUFACTURE    OF    CE-LLULOlSiE. 


blocks  are  then  transported  to  a  higher  floor  to  be  still 
more  diminuted.  Some  manufacturers  at  this  stage  ha,ve 
the  knots  bored  out,  because  as  these  do  not  become  soft 
in  boiling  they  do  not  yield  cellulose,  and  further  the  fibre- 
ous  parts,  laying  next  to  the  knots  as  a  rule  remain  hard, 
or  at  least  yellow.  Even  by  boring  them  out,  they  cannot 
be  removed  entirely,  so  that  it  seems  advisable  not  to  sort 
them  out  until  later.  The  diminution  of  the  wood,  neces- 
sary for  the  more  thorough  action  of  the  leach  in  the 
subsequent  boiling  may  now  either  be  done  with  circular 
saws  which  cut  the  blocks  into  slices  of  25  to  30  mm. 
thickness,  or  by  chip — or  cut — machines.  In  the  former 
case  according  to  the  capacity  of  the  plant  a  larger  number 
of  ordinary  single  circular  saws  or  those  with  several  saw- 
blades  in  a  row  are  used  as  a  rule.  Because  the  labor  of 
feeding  has  to  be  done  by  hand  and  accidents  to  those  em- 


FIG.   fi. 

ployed  therein  may  easily  happen,  it  is  necessary  to  pro- 
vide all  possible  safety  arrangements  and  especially  caps 
over  saws.  In  order  that  the  operatives,  who  mostly  do 
the  sawing  by  contract,  do  not  make  the  slices  larger  than 
desired,  it  is  advisable  to  fasten  to  the  table  in  front  of  the 
saw  a  small  angle  iron,  which  stands  sideways  about  25  to 
30  mm.  off  the  saw-blade  and  answers  as  a  guide.  The 
shorter  the  block  becomes  the  greater  the  danger  for  the 
operative/  if  he  presses  the  block  against  the  saw  with 
naked  hand.  If  the  operative  uses  a  short  piece  of  wood 
with  a  handle  on  one  and  several  steel  points  in  the  other 
end,  which  he  pushes  every  time  in  the  head  of  the  block 
to  be  cut,  he  can  thus  easily  guide  the  block  and  the  dan- 
ger of  possible  injury  is  almost  excluded. 

In  using  circular  saws  it  is  very  important  to  take  care 
that  the  saw  blades  are  thin,  the  best  possible,  and  that  the 


THE    MANUFACTURE    OP    CELLULOSE.  17 

set  of  the  points  of  the  teeth  of  the  saw  (the  spreading)  to 
the 'right  or  left  is  just  so  much,  that  the  saw  does  not 
get  clogged  in  cutting.  .  The  waste  of  sawdust,  even  with 
observance  of  the  precaution  mentioned,  is  very  large  in 
proportion,  and  may  increase  if  these  directions  are  not 
followed.  When  slices  of  25  to  30  mm.  thickness  are  to  be 
cut,  in  every  log  of  1  m.  length  at  least  33  cuts  have  to  be 
made,  and  when  for  each  of  them  but  4  mm.  loss  is  admit- 
ted, the  result  is  132  mm.  per  thousand,  or  13  per  cent. 
Though  this  waste  appears  very  clean,  it  yet  contains  many 
small  particles  of  knots,  yielding  brown  spots  in  the  cellu- 
lose, if  too  high  demands  are  not  made  on  the  product,  the 
dust  may  be  filled  in  the  boiler  together  with  the  slices,. 
the  whole  or  part  of  it  mixed,  but  care  should  be  taken 
that  it  is  placed  in  about  the  middle  of  the  total  charge :  of 
the  boiler  so  that  in  discharging  the  leach  it  would  not. 
clog  the  valves,  or  when  swimming  on  top  it  would  not 
spoil  the  whole  operation.  It  would  certainly  be  better  to 
leave  out  the  dust  entirely,  or  at  least  to  use  it  together 
with  low  grade  wood  for  a  cheaper  quality.  At  this  point 
may  be  mentioned,  that  lately  the  shavings  from  barking, 
especially  such  not  charged  with  brown  bark,  are  boiled 
into  cheap  cellulose  by  some  manufacturers.  Because,  in 
proportion  to  their  weight,  not  many  can  be  filled  into  the 
boiler,  they  are  cut  by  a  chopping  machine  into  short  frag- 
ments, which  often  being  charged  into  the  boiler  are  trod- 
den down  by  a  laborer,  so  that  the  yield  in  cellulose  in 
each  operation  is  but  10  to  15  per  cent,  less  than  in  an 
operation  with  good  wood.  In  this  manner  the  working 
of  shavings  is  made  profitable,  while  previously  they  were 
mostly  used  as  fuel.  Mixed  with  sawdust  or  waste  from 
pulp  milling,  they  may  also  be  worked  into  lesser  grades 
of  wood  fibre.  It  may  also  be  mentioned  that  with  the 
above  described  methods  of  cutting  wood,  the  knots  exist- 
ing in  the  different  slices  are,  as  a  rule,  not  sorted  out  be- 
fore boiling,  because  the  smaller  ones  could  not  all  be 
picked  out  by  any  means,  and  sorting  after  boiling  would 
still  be  necessary.  After  the  wood  is  softened  by  boiling, 
every  knot  can  be  detected  with  the  finger  and  easily 
picked  out. 

When  a  chipping  machine  is  used  in  reducing  the  wood 

to  be  boiled  the  disadvantage  of  great  loss  of  saw  dust  is 

.eliminated,  because  the  previous  barked  wood  is  hewn  off 


18  THE    MANUFACTURE    OF    CELLULOSE. 

the  head  in  somewhat  oblique  direction  in  fragments,  meas- 
uring about  30  mm.  In  consequence  of  the  forcible  bear- 
ing away  the  particles  also  receive  cracks  in  all  possible 
directions,    thus   becoming   loosened   and   permitting   the 
leach  to  permeate  them  in  the  subsequent  boiling.     The 
main  part  of  such  chipping  machine  is  a  heavy  oast  iron 
wheel  of  1,400  mm.  diameter  on  a  strong  horizontal  shaft. 
To  prevent  springing  a  ring  of  forged  iron,  50  mm.  wide, 
is  fastened  around  it  while  warm.     Near  the  circumfer- 
ence one  or  two  strong  knives  are  fastened,  each  by  nine 
screws,  which  stand  a.bout  5  mm.  off  the  wheel  and  which 
move  quite  rapidly  on  a  stationary  support,  over  which  the 
wood  to  be  cut    is    introduced.     When    lighter    wood    is 
worked   the   previously   hand-barked   pole   is   fed   to    the 
machine  by  two  men,  and  must  be  turned  about  after  each 
out.    Another  laborer  shovels  the  chips  upon  the  elevator, 
which  takes  them  to  the  upper  lofts.    The  machine  natur- 
ally requires  much  power  and  because  it  continuously  re- 
ceives heavy  shocks,  it  is  best  to  place  it  on  the  ground 
•loor,  and  as  stated,  to  transfer  the  cut  wood  upwards.  The 
machine  is  capable  of  chipping  in  12  hours  about  35  cubic 
meters  of  wood  from  the  head  of  poles  about  2J  m.  long. 
In  some  factories,  however,  the  machine  is  placed  in  up- 
per lofts;  the  wood  is  in  short  pieces,  previously  peeled  on 
the  barking  machine,  and  the  blocks  are  put  on  an  end- 
less band  and  automatically  led  to  the  chipping  machine. 
The  wood,  reduced  as  described  above,  is  moderately  filled 
into  the  boilers  in  cases  where  the  factory  does  not  work 
prime  cellulose.     In  most  cases,  however,  it  is  first  assort- 
ed by  a  number  of  boys  or  girls.     For  this  purpose  it  is 
thrown  upon  a  sifting  table,  where  dirt  and  very  small 
chips  fall  through  and  every  piece    containing    a    knotty 
part,  is  sorted  out  by  hand.     This  method  is  quite  expen- 
sive, and  in  each  case  particular  care  should  be  taken  in 
calculating  whether  the  cost  of  labor  for  sorting  is  recov- 
ered by  the  production  of  a  high  grade  and  pure  cellulose. 
A  later  design  of  a  chipping  machine,  described  in  the 
Papier   Zeitung,     originates    from    geh.      Commerzienrat 
Albert  Methammer  and  seems  to  be  based  on  the  prin- 
ciple of  pencil  sharpening.     By  this"  method  the  wood  is 
not  cut  directly  across  the  grain  as  in  some  machines,  but 
is  sliced  off  in  long  chips.     In  this  manner  the  machine 
requires  less  power  and  has  to   suffer  much  less  violent 


THE    MANUFACTURE    OF    CELLULOSE. 


19 


shocks.  The  cutting  away  almost  vertically  on  the  long 
axis  of  the  wood  is  not  desirable  on  account  of  the  large 
consumption  of  power.  As  a  rule  an  angle  of  45°  is  ac- 
cepted as  the  most  effective,  for  where  the  wood  is  cut  at 
that  angle  the  cells  are  opened,  and  the  wood  inside  is 
crushed  and  loosened  to  such  extent  that  the  leach  can 
enter  easier  and  quicker.  Whether  the  knife,  which  does 
the  principal  work,  and  which  in  this  machine  had  to  be 
made  thin,  has  worked  well,  is  not  known  to  the  author. 


FIGURE   7. 

The  entire  construction  can  be  learned  from  figures  7,  8, 
9  and  10  and  from  the  following  description: 

Fig.  7  presents  the  front  view,  fig.  8  the  side  view,  with 
part  cut,  fig.  9  the  view  from  above  (the  plane),  fig.  10 
shows  in  enlarged  scale  the  knife  holder  with  knife. 

The  frame  A,  in  which  is  the  cranked  driving  shaft,  de- 
velopes  upward  into  a  stand  A7,  the  front  face  of  which  is 
inclined.  To  the  stand  A'  the  adjustable  guiding  'posts  n 
are  fixed,  along  which  a  sled  f  can  be  moved  up  and  down 


20  THE    MANUFACTURE    OP    CELLULOSE. 

The  latter  carries  the  knife  a,  with  the  frame  d  (fig.  10), 
covering  it  at  the  edge.  With  the  knife-sled  f  is  con- 
nected a  cross  beam  1,  to  which  are  connected  the  two 
driving  rods  m,  linked  to  the  crank  of  the  driving  shaft  B. 
On  the  right  and  left  of  the  shaft,  outside  of  the  bearing 
boxes  are  the  fly  wheels  D  and  Dl,  one  of  which  serves  as 
driving  pulley.  Alongside  of  this  is  the  loose  pulley  D2. 
It  is, at  once  evident  that  the  sled  f  with  the  knife  and  the 
cover-frame  in  one  turn  of  the  shaft  B  makes  a  lift  along 
the  inclined  face  of  the  frame  Al  corresponding  to  double 
the  length  of  the  eccentricity  of  the  shaft  crank.  By  using 


FIGURTC   8. 

two  connecting  rods,  cornering  of  the  knife-sled  f  at  the 
adjustable  leaders  n  is  prevented.  The  log  is  fed  upon  a 
table  C  in  a  direction  oblique  to  the  axis  of  the  shaft  B, 
but  in  level  position,  so  that  the  line  of  the  cut  is  inclined 
to  the  long  axis  of  the  fibre,  as  well  as  to  its  perpendicular, 
and  thus  the  fibres  are  cut  through  in  a  doubly  inclined 
direction. 

To  obtain  undamaged  slices  the  knife  has  to  be  very  thin, 
and  to  give  to  the  thin  knife  (fig.  9)  sufficient  resistance 
and  stiffness,  it  is  fastened  to  the  knife  support  f,  not  only 
with  its  upper  edge,  but  also  with  both  sides  with  screws, 


THE    MANUFACTURE    OP    CELLULOSE. 


21 


and  the  latter  as  well  as  the  frame  d,  covering  the  upper 
side  of  the  knife,  are  for  this  purpose  cut  out  in  a  semi- 
circular form. 

The  knife,  the  edge  of  which  is  somewhat  beveled,  does 
not  cut  against  a  stationary,  so  called  stock-knife,  but  en- 
ters in  its  lowest  position  into  a  correspondingly  wide  slit 
of  the  log  support.  The  automatic  advancing  of  the  log  is 
secured  by  means  of  two  pairs  of  rollers,  upon  one  of  which 
lays  the  log,  while  the  second  pair  of  rollers  (o)  holds  the 
log  in  the  proper  position  from  above. 


FIGURE  9. 

The  feed  is  broken  during  about  one-quarter  of  the  revo- 
lution and  is  going  on  only  when  the  knife  has  accomplish- 
ed the  upper  part  of  the  motion.  In  this  manner  it  is  pos- 
sible to  cut  logs  of  a  diameter  equal  to  three-fourths  of  the 
lift  of  the  knife.  This  periodic  feeding  is  secured  by  the 
eccentric  (g),  which  is  fixed  to  the  shaft  B  and  upon  which 
runs  a  roller  (h),  borne  in  the  arm  (p)  of  an  angle-lever 
(pr),  turning  about  the  pin  (q).  The  second  arm  (r)  of  this 
lever  is,  by  the  car  (s),  which  is  provided  with  a  universal 
joint,  connected  with  one  arm  (t)  of  the  angle-lever  (ttl); 
the  second  arm  (tl),  by  the  push-bar  (si),  also  provided  with 
universal  joint,  is  likewise  connected  with  the  lever  (u). 


22 


THE    MANUFACTURE    OP    CELLULOSE. 


When  the  pulley  (h)  is  lifted  by  eccentric  (g)  the  bar 
(si)  (fig.  8  and  9)  is  pushed  to  the  right  and  hence  the  two 
levers  (uul),  which  are  connected  together  by  the  push-car 
(v),  also  stick  to  the  right  with  their  upper  ends.  On 
the  upper  ends  of  these  levers  are  friction  latches  (wwl), 
provided  with  rollers,  which  trail  upon  the  edged  disks  (xxl) 
in  a  way  that,  with  the  above  mentioned  swinging  to  the 
right  of  the  lever  ends  the  disks  (xxl)  are  carried  along. 
With  the  swinging  to  the  left  of  the  lever  ends,  the  latches 


FIGURE  10. 

(wwl)  slide  back  over  the  final  rollers.  The  levers  (uul) 
turn  loosely  on  the  spindles  of  the  disks  (xxl).  The  spindles 
bear  the  rollers,  which  support, 'the  log  from  below,  so  that 
with  every  turn  of  the  disks  (xxl)  this  pair  of  rollers  will  al- 
so turn,  and  thus  the  log  is  correspondingly  pushed  forward. 
The  end  of  the  bar  (si)  at  its  connection  with  the 
lever  (u)  slides  in  a  groove  by  which  means  the  amount  of 
feed  can  be  regulated.  The  pulley  (h)  running  on  the  ec- 
centric (g)  follows  the  latter  when  the  number  of  revolu- 
tions is  low,  but  when  80  to  90  per  minute  the  molecular 


THE    MANUFACTURE    OF    CELLULOSE.  23 

forces  act  hinderingly,  and  the  pulley  does  not  follow  the 
delivery  of  the  eccentric  curve  with  sufficient  quickness. 
To  avoid  the  shocks  which  would  result,  a  spiral  spring  (i) 
is  arranged,  which  with  one  end  is  fastened  to  the  angle- 
lever  (pr),  and  with  the  other  to  a  spiral  wheel  (y),  which 
is  in  action  with  a  second  spiral  (2),  put  in  rotation  by 
means  of  a  key,  so  that  the  spiral  spring  can  be  suitably  ad- 
justed to  give  the  necessary  acceleration  to  the  pulley.  A 
small  roller  (r),  borne  in  one  end  of  a  toothed  bar,  serves 
to  hold  down  the  log  before  the  knife. 

In  conclusion  the  author  has  computed  a  table  from 
practical  observations,  to  ascertain  whether  it  is  of  more 
advantage  in  the  manufacture  of  cellulose  to  use  light  or 
heavy  logs.  These  values  refer  to  the  first  mentioned  case, 
where  the  wood  is  cut  into  slices  by  the  circular  saw. 


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28.26 

34.2 

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3936 

63.6 

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10     100 

31.4 

31.4 

200 

3200 

78.5 

25.12 

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59 

4.91 

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47.1 

20.7 

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1408 

176.5 

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51 

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20       25 

62.8 

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800 

314.0 

25.12 

3.6 

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12.5 

32 

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489.8 

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6.25 

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18.5 

112 

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269 

907.4 

22.4 

34.0 

152 

12.7 

This  computation  is  not  quite  carried  in  practice,  as  for 
instance  for  woods  of  10  m.  thickness,  10x10  100  pieces  are 
set  in  1  square  meter.  With  close  observation  one  may 
learn  from  this  table  that  with  thinner  wood,  the  surface 
to  be  barked,  and  consequently  the  waste  is  the  largest; 
therefore  it  would  be  of  advantage  to  work  only  very  thick 
trees,  if  prices  were  the  same.  The  cross  section  really  to 
be  cut  in  one  volumeter  of  wood  is  almost  equal  in  thick 
and  thin  wood,  namely,  about  25  sq.  m.,  whereas  the  work- 
ing time  necessary  to  cut  one  volumeter  of  wood  of  light, 
medium  and  heavy  quality  into  slices  of  30  mm.  thickness 
differs  greatly.  It  is  the  great  number  of  the  necessary 


24 


THE    MANUFACTURE    OF    CELLULOSE. 


cuts  and  the  loss  of  time  between  the  single  cut  in  thin 
wood  which  makes  its  use  unprofitable;  while  in  very  heavy 
wood  the  saw  meets  too  much  resistance,  becomes  clogged, 
goes  slower  and  takes  considerably  more  time  to  do  the 
game  work.  But  as  time  is  money  and  very  heavy  logs 
have  a  higher  timber  value,  their  use  is  not  recommended. 
The  table  shows  plainly  that  it  is  the  most  profitable  to 
buy  medium  heavy  wood  of  about  20  cm.  diameter.  As  a 
consequence  of  the  continually  increasing  competition  and 


FIGURE  11. 

the  increased  demands  of  the  wood  fibre  consumers  many 
changes  have  taken  place  in  recent  years,  in  the  working 
of  the  wood,  which,  without  regard  to  the  different  patent 
processes  in  the  manufacture  of  cellulose  have  found  ad- 
mittance uniformly  in  the  factories  of  the  different  sys- 
tems, as  it  is  now  the  main  object  to  save  as  much  as  pos- 
sible in  power  and  labor,  as  well  as  to  manufacture  a  pro- 
duct as  pure  as  possible.  A  plant  already  introduced  in  a 
great  number  of  factories  by  the  foundry  and  machine 
works  (formerly  Goetjes  &  Schulze  in  Bautzen,  fulfills 


THE    MANUFACTURE    OP    CELLULOSE. 


2fi 


these  conditions,  and  the  machinery  previously  used  has 
been  connected  with  the  new  and  shaped  into  a  practical 
whole.  In  the  process  the  logs  are  cut  by  a  log-saw  in 
blocks  of  1  m.  or  less  as  already  described.  These  are 
barked  by  a  single  or  double  barking  machine  and,  when 
heavy  wood  is  used  they  are  also  split  by  a  splitting  ma- 
chine, such  as  are  in  use  in  wood  pulp  factories.  This 
splitting  is  for  the  purpose  of  facilitating  the  work  of  the 
chipping  machine^  because  the  hewing  of  the  chips  off 
heavy  logs  requires  decidedly  more  power  than  off  a  thin 
one.  The  chipping1  machine,  as  already  mentioned,  is  at 


FIGURE  12. 


present  usually  built  with  two  knives  and  the  feeding  of 
the  wood  is  not  as  originally  practiced,  oblique  to  the 
horizontal  and  vertical  to  the  ground  section  of  knife 
blades,  but  oblique  to  both  directions,  as  shown  in  figures 
11  and  12. 

Thus  the  cutting  of  the  chips  is  done  along  the  long  axis 
of  the  wood,  which  is  naturally  easier,  than  hewing  of  the 
head  wood.  The  feed  arrangement  is  obtained  by  a  semi- 
circular gutter,  which  is  cast  to  the  frame  and  in  which  the 
log-pieces  are  placed,  being  fed  to  the  knives  by  their  own 
weight.  As  the  knives  are  500  mm.  long  and  150  mm. 


2&  THE    MANUFACTURE    OF    CELLULOSE. 

wide  as  a  rule,  two  guiding  gutters  alongside  each  other  are 
provided,  so  that  two  logs  may  be  cut  at  the  same  time. 
When  care  is  taken  that  the  knives  are  always  sharp^  which 
necessitates  a  change  every  two  hours,  such  chip  machine 
can  in  twelve  hours  out  as  much  wood  as  is  needed  for  a 
daily  production  of  6,500  kgr.  of  dry  cellulose.  This  re- 
peated changing  of  the  knives  is  further  to  be  recommend- 
ed, because  of  the  fact  that  they  get  warm  in  the  working. 


FIGURE  13. 

The  chips  hewn  off  then  fall  below  the  machine  directly 
upon  a  wide  band,  moving  slowly  along,  and  carry  the  wood 
to  the  so-called  breaker.  On  the  way  there  the  principal 
and  largest  knots  are  sorted  out.  Contrary  to  Professor 
Mitscherlich,  who  has  recommended  the  cutting  into  slices, 
Dr.  Karl  Kellner  has  found  from  the  beginning'  that  the 
most  thorough  splitting  of  the  wood  fragments  is  of  ad- 
vantage in  permitting  the  entrance  of  the  leach,  and  there- 


THE    MANUFACTURE    OF    CELLULOSE. 


27 


fore  was  not  satisfied  with  the  effect  of  the  chipping  ma- 
chine alone,  but  besides  uses  the  breaker,  which  is  con- 
structed after  the  common  coffee  mill,  as  shown  in  fig.  13. 
The  chipped  wood,  which  in  consequence  of  the  force  and 
strain  of  the  chipping  is  already  full  of  minute  cracks,  is 
fed  by  the  elevator  to  the  funnel,  into  the  casing  (g),  which 
is  conical  in  shape,  widening  towards,  the  bottom.  The 
wall  of  the  casing  is  provided  with  sharp  teeth  and  within 
a  smaller  cone  K,  also  set  with  teeth,  is  revolving  rapidly. 
The  distance  between  the  stationary  and  movable  parts  is 
so  proportioned  that  the  chips  of  wood  are  considerably  re- 


FIGURE  14. 

duced  in  size,  while  the  harder  knots  fall  through  unbroken. 
In  place  of  this  breaker  the  centrifugal  machine  has  been 
lately  used  with  success.  It  is  claimed  to  work  more  ad- 
vantageously because  it  does  not  tear  the  fragments  so 
much,  and  renders  easier  the  separation  of  the  knots  and 
knotty  parts  from  the  sappier  wood.  A  cross  section  of 
the  characteristic  parts  is  shown  in  fig.  14,  and  in  fig.  15 
the  front  view. 

Inside  of  a  casing,  on  the  front  wall  round  pins  of  forged 
iron  are  set  in  two  concentric  rings,  between  which  two 


28 


THE    MANUFACTURE    OF    CELLULOSE. 


smaller  rings  of  pins  are  rapidly  moving.  These  latter 
mentioned  pins  are  set  in  a  round  disk,  which  is  wedged 
on  a  horizontal  shaft.  The  elevator  throws  the  chips  of 


FIGURE  15. 

wood  into  the  flat  pipe  (a)  cast  to  the  front  wall,  from 
where  they  enter  immediately  over  the  shaft  into  the 
middle  of  the  apparatus,  get  caught  by  the  pins  of  the 


FIGURE  16. 

rapidly  rotating  disk  (about  1,000  revolutions  per  minute), 
thrown  around,  crushed  and  separated    from    the   knots. 


THE    MANUFACTURE    OF    CELLULOSE.  29 

Through  an  opening  in  the  case  the  wood  then  falls  upon 
an  elevator  band  below,  which  carries  it  further  to  the  ro- 
tating apparatus. 

For  a  quantity  of  6,500  kilos  of  dry  cellulose  supposed 
to  be  worked  per  day,  this  machine  consists  of  two  conical 
drums  of  6  to  7  m.  long  and  about  2  m.  in  diameter,  the 
constructions  of  which  is  shown  in  fig.  16  and  17.  The 
drums,  made  of  wooden  rings,  rest  in  the  front,  rear  and 
eventually  in  the  middle  upon  two  driving  rollers  each, 
which  rotate  rapidly,  the  large  drums  making  about  12 
revolutions  per  minute.  The  inside  of  the  wooden  frame 
work  is  lined  with  perforated  sheets,  thus  forming  a 
smooth,  large  funnel,  into  the  smaller  end  of  which  the 
fine  wood  is  carried  by  the  elevator.  By  rotation  of  the 
cone  the  wood  is  carried  up  part  of  the  circumference,  and 


.-.-_:  :;-j-i--::-.:-~-.--n.-::.;-~:-.:.-!i~-:  --' 


///////////////^ 

FIGURE  17. 

thus  slides  along  the  smooth  wall  towards  the  wider  end 
of  the  funnel,  or  falls  through  the  numerous  openings 
under  the  drum.  Because  it  must  perform  at  the  same 
time  a.  cleaning,  as  well  as  a  sorting  of  the  pieces  according 
to  size,  and  possibly  also  a  separation  of  the  knots,  the  fore- 
most smaller  part  of  the  drum  lining  has  fine  holes  of 
about  6  mm  diameter,  a  second  part  has  larger  openings  and 
the  third  part  at  the  wide  of  the  funnel  has  the  'normal 
openings,  which  answer  the  size  of  the  good  pieces  to  be 
worked.  Below  the  first  and  second  department  are 
boxes  closed  by  doors,  in  which  the  sifted  material  accumu- 
lates. This  consists  in  No.  1  of  dust,  splinters,  knotty 
particles  and  fine  black  knots  and  is  either  used  in  the  fac- 
tory for  kindling,  or  sold  for  other  purposes;  No.  2  con- 


30  THE    MANUFACTURE    OF    CELLULOSE. 

tains  medium  sized  pieces,  mixed  with  some  knotty  parts 
and  when  enough  has  accumulated,  it  is  separately  worked 
into  second  quality  ware.  The  good  wood  from  No.  3  falls 
upon  a  band  about  I  m.  wide,  which  is  at  a  right  angle  to 
the  drum,  and  carries  its  load  slowly  along,  serving  as  a 
table,  at  both  sides  of  which  girls  are  standing,  who  sort 
out  all  pieces,  which  still  contain  knots.  The  main  part 
of  knots  will  be  larger  than  the  opening  for  the  good  wood 
and  at  the  wider  end  of  the  funnel  drops  into  a  basket.  The 
contents  of  this  basket  naturally  is  again  gone  over  and 
larger,  but  clean  pieces  of  wood,  are  sorted  out  to  be  fur- 
ther worked.  Because  the  use  of  elevators  saves  much 
hand  labor,  one  or  more  other  elevators  now  expedite  the 
wood  to  a  floor  above  the  boilers  into  boxes,  the  capacity 
of  which  corresponds  to  the  boilers  below. 

LEACHES  AND  LEACHEMAKING;  THE  SODA  PROCESS. 

As  the  name  suggests,  soda  is  used  in  the  soda  process, 
as  leach  in  boiling.  Originally  this  was  in  the  form  of 
carbonate  of  soda,  made  caustic  by  adding  lime,  in  order 
to  dissolve  'the  incrusting  constituents  of  the  wood  fibre 
and  to  separate  them  from  the  pure  fibre.  In  itself  the 
soda  does  not  make  the  solution  effective,  but  water  must 
be  present  and  a  high  temperature  must  be  employed.  The 
hot  steam  alone  renders  some  of  the  incrusting  constit- 
uents soluble,  and  thus  other  products  are  formed,  also 
acids,  which  have  dissolving  qualities,  but  would  have  an 
injurious  influence  on  the  fibre  itself,  were  it  riot  for  the 
iact  that  the  presence  of  the  soda  neutralizes  them  while 
the  process  of  boiling  is  still  going  on.  This  depends 
principally  on  the  proper  strength  of  the  leach  and  main- 
taining the  necessary  temperature  (corresponding  to  the 
pressure  of  the  steam  in  atmosphere)  also  the  length  of 
time  for  the  process  of  boiling  in  proportion  to  the  quan- 
tity of  the  wood  and  its  quality.  It  is  quite  natural  that 
the  most  diverse  statements  were  made  about  this  before 
practical  experience  has  established  proportional  values. 
Professor  Hager  wrote  in  this  regard  the  following:  "In 
1869  a,  tension  of  4,  5  atmospheres  (150°  C)  was  consid- 
ered sufficient  by  Keegan,  while  Lee  in  1870  went  up  as 
high  as  11  atmospheres  (210°  C) — lingerer  in  1872  has  as- 
serted that  a  pressure  of  from  3  to  4  atmospheres  (134°- 
144°  C)  for  leaved  wood  and  from  5  to  G  atmospheres 


THE    MANUFACTURE    OF    CELLULOSE.  31 

(152°-159°)  for  pine  wood  answers  the  purpose,  while 
Kosenham  in  1878  again  stated  that  10  atmospheres  (180° 
C)  was  correct.  The  statements  by  Urgerer  seem  to  fit 
the  purpose  best.  However  an  account  of  the  great  risks, 
presented  by  the  high  tension  in  boilers  of  such  immense 
dimensions,  the  pressure  of  10  atmospheres  (180°  C  boil- 
ing temperature)  should  not  be  exceeded.  In  similar  man- 
ner, the  quantities  of  soda  employed,  and  the  strength  of 
the  leaches  deviate.  According  to  the  patent  of  Wott  & 
Burgess,  the  leach  is  made  12°  B  strong,  of  which  so  much 
is  taken  that  to  100  parts  of  wood,  considered  dry,  fcl  parts 
of  soda  of  60$  purity  are  used.  Sinclair  has  used  25  parts 
of  soda  for  100  parts  of  wood,  in  a  solution  of  140°  B.  Ac- 
cording to  lingerer,  and  employing  his  system  a  leach  will 
do,  of  which  4-5$  of  caustic  soda  of  60$  purity  is  used  with 
leaved  wood  and  6-8$  to  pine  wood.  Much  less  varying 
are  the  statements  about  the  time  of  boiling,  which  as  a 
rule  is  stated  at  from  5  to  6  hours  for  one  operation." 

These  reports  by  Professor  Hager,  in  conformity  with 
communications  to  the  author,  are  to  be  corrected  by  the 
statement  that  a  pressure  of  4  1-2  atmospheres  is  by  no 
means  sufficient  in  the  production  of  soda-cellulose;  and 
on  the  other  hand,  that  until  1870  Lee  has  not  been  em- 
ployed in  the  task  of  making  wood  fibre,  and  also  that  up 
to  1872  lingerer  had  not  yet  boiled  cellulose.  Besides 
the  latter  had  not  employed  5  to  6,  but  8  to  10  atmos- 
pheres of  pressure.  It  is  mentioned  conclusively  that 
"ringer's  process  has  not  proved  so  well  in  practice,  as  was 
expected.  The  author  is  not  personally  able  to  render 
judgment  in  this;  theoretically  the  process  is  well  consid- 
ered. The  same  writer  further  makes  remarks  about  the 
nature  and  solubility  of  the  organic  constituents  of  wood, 
which  are  very  interesting  and  by  which  is  shown  the  suc- 
cessive work  of  the  leach.  He  says:  "The  organic  con- 
stituents of  the  wood  belong  to  several  groups,  as  some 
of  them  are  soluble  in  water  and  consequently  can  be  re- 
moved from  the  wood  by  treating  with  water,  while  others 
are  insoluble  in  water.  To  the  former  belong  gum,  veg- 
etable albumen,  tannins,  coloring  matter,  etc.,  to  the  latter 
belongs  the  resins,  balsams,  etc.  Lastly  there  is  the  in- 
crusting  matter^  or  the  lignin,  which  has  been  deposited 
in  and  upon  the  membranes  of  the  cells  and  vessels  and 
which  is  consequently  most  closely  combined  with  the 


32  THE    MANUFACTURE    OF    CELLULOSE. 

cellulose.  A  wood  fibre  may  therefore  be  conceived 
as  built  up  with  the  cellulose  as  the  elementary  substance, 
penetrated,  with  lignin,  next  with  a  covering  layer  of  resins, 
etc.,  insoluble  in  water  and  finally  a  third  layer,  which 
mainly  contains  substances  soluble  in  water.  This  com- 
position justifies  the  conclusion  that  every  layer  protects 
more  or  less  the  one  laying  below,  against  the  action  of  the 
solvents,  and  that  removing  the  layers  in  reversed  order 
must  lay  bare  the  cellulose.  Now,  as  the  outer  layer  is 
soluble  in  water,  it  is  sufficient  to  treat  the  wood  first  with 
water  or  steam  of  such  temperature,  that  no  change  of  the 
lignin  can  take  place.  Because  the  resins  dissolve  in  weak 
leaches,  the  application  of  such  removes  the  second  layer, 
while  the  lignin  is  treated  with  stronger  leaches  at  high- 
er temperatures.  Upon  this  principle,  lingerer  in  Vienna 
has  worked  out  a  process  of  boiling,  which  must  be  con- 
sidered the  most  perfect,  because  it  treats  the  wood  in  suc- 
cession with  steam  and  leaches,  the  concentration  and  tem- 
perature of  which  are  continuously  being  raised,  whereby 
it  at  the  same  time  the  leach  is  worked  to  exhaustion  and 
excellent  fibres  is  produced." 

This  system  shall  be  described  more  particularly  in  the 
next  chapter.  Here  we  have  next  to  do  with  the  leach  and 
its  preparation,  which  is  very  simple  in  the  soda  process,  as 
soda  and  the  other  chemicals  are  simply  dissolved  in  a 
tank,  in  which  by  means  of  a  steam  coil  the  liquid  can  be 
heated  and  then  so  diluted  that  the  desired  degree  of  con- 
centration is  obtained.  But  as  soda  is  expensive,  and  as 
it,  would  be  extravagant  to  let  it  run  to  waste  together  with 
the  spent  leach  the  idea  was  conceived  soon  after  soda- 
cellulose  manufacturing  was  introduced,  to  evaporate  the 
leach  containing  all  the  incrusting  constituents  of  the 
wood  fibre,  and  thus  to  regenerate  the  soda,  whereby  at  the 
same  time  the  otherwise  inevitable  contamination  of  the 
waters  was  avoided.  Naturally  the  soda  is  not  recovered 
pure,  several  combinations  being  formed,  but  it  was  dis- 
covered that  the  same  action  results  from  the  intermediate 
product  of  the  soda  manufacture,  the  sulphate  of  soda  as 
from  the  carbonate  of  soda.  Dahl  in  Danzig,  discovered 
this  about  1883  and  he  first  used  a  leach  containing  sul- 
phate of  soda,,  carbonate  of  soda,  caustic  soda  and  sulphide 
of  soda.  The  leach  is  prepared  from  sulphate  of  soda,  and 
23-25^  of  caustic  lime,  to  which  are  added  the  salts  re- 


THE    MANUFACTURE    OF    CELLULOSE.  33 

covered  from  former  leaches.  The  spent  leaches  are  con- 
centrated by  evaporation,  strongly  calcined  and  after  all 
gases  are  driven  off,  pulled  out  of  the  furnace  in  the  form 
of  coke.  The  mass  is  then  lixivated  and  the  solution  ob- 
tained serves  to  make  new  leach.  To  obtain  it  free  from 
coal,  the  concentrated  solution  is  heated  in  a  furnace  to 
dark  redness.  The-  resulting  mass,  assuming  a  reddish- 
brown  color  in  cooling,  is  easily  soluble  in  water  and  has 
about  the  following  composition: 

Sulphate  of  Sodium  16$ 

Carbonate  of  Sodium  50$ 

Caustic  Soda  (soda)  20$ 

Sulphide  of  Sodium  10$ 

Different  other  substances  4$ 

This  composition  varies  considerably  according  to  the 
wood  treated,  but  the  solving  power  of  the  leach  is  not 
much  influenced.  These  salts  recovered  from  the  leach 
must  be  dissolved  soon  to  avoid  the  action  of  the  atmos- 
phere. In  the  boiling  and  recovering,  about  10  to  15$  of 
the  salts  contained  in  the  leach  get  lost,  and  must  be  re- 
placed with  sulphate  of  soda.  From  85  to  90$  of  the  re- 
covered salts  and  15  to  16$  of  sulphate  of  sodium,  which 
has  been  boiled  with  20  to  23$  of  caustic  lime,  yield  a  good 
leach.  The  quantity  of  the  sulphate  of  soda  treated  with 
lime,  and  the  quantity  of  lime  itself  vary  with  the  esti- 
mated loss  of  the  salts.  At  a  loss  of  10$,  10  kilos  of  sul- 
phate of  sodium  and  20  kilos  of  lime  are  necessary  for  every 
90  kilos  of  the  recovered  salts.  At  a  loss  of  15$,  for  every 
85  kilos  of  the  salts,  15  kilos  sulphate  of  sodium  and  23  kilos 
of  lime  have  to  be  used;  at  a  loss  of  20$,  for  every  80  kilos 
of  the  salts,  20  kilos  of  sulphate  of  sodium  and  25  kilos  of 
lime.  In  general  the  resulting  leach  contains  about  37# 
of  sulphate  of  sodium,  8$  of  carbonate  of  sodium,  24$  of 
caustic  soda  and  3$  of  sulphite  of  sodium.  From  the 
above  it  will  be  seen  that  the  process  described  differs  from 
the  older  process  of  boiling  with  caustic  soda  in  that  in 
preparing  the  leach,  the  caustic  soda  lost  in  boiling  and  re- 
covering of  the  salts  is  replaced  by  sulphate  of  sodium,  in- 
stead of  by  caustic  soda,  and  the  quantity  of  the  caustic 
lime  used  is  reduced  from  45$  to  from  20  to  23$. 

As  in  other  lines  of  manufacture,  competition  has  com- 
pelled economies,  especially  since  sulphite-cellulose  has 
made  its  appearance.  In  the  course  of  time  they  substi- 


34  THE    MANUFACTURE    OF    CELLULOSE. 

tute  the  cheapest  grades  in  the  market  for  the  expensive 
sulphates1  free  from  acid  and  iron,  first  used  "because  iron 
and  free  sulphuric  acid  could,  according  to  the  manner  in 
which  the  sulphate  was  employed  in  the  different  factories, 
either  be  made  harmless  in  the  form  of  sulphate  of  iron 
and  sulphate  of  lime  by  the  caustic  process,  or  when 
worked  with  the  sto>ck  for  calcination  in  the  fire.  Several 
works>  fortunately  situated  in  the  neighborhood  of  dyna- 
mite factories,  went  over  to  the  use  of  the  waste  product 
of  these  factories;  the  acid  sulphate  of  sodium.  This  salt 
being  nothing  else  then  sulphate  of  sodium  with  consid- 
erable percentage  of  free  sulphuric  acid,  which,  as  already 
mentioned,  can  be  removed  by  chemical  process  or  even 
made  useful.  In  general,  however,  this  utilization  of  the 
acid  sulphate  in  the  manufacture  of  soda  wood  fibre  is  not 
a  characteristic  modification  of  the  process  of  Dahle,  which 
in  the  manufacture  of  soda-cellulose  is  now  in  general  use. 
According  to  Dr.  Frank  this  utilization  of  sulphuric  acid 
can  be  done  by  adding  chloride  of  sodium,  consequently 
is  utilized  as  sulphate  of  sodium.  In  the  customary  pro- 
cess of  neutralizing  with  lime  the  sulphuric  acid  does  but 
add  a  ballast  of  sulphate  of  calcium  (gypsum),  therefore 
neutralization  with  spent  leach  would  be  still  better. 

At  this  point,  after  concluding  the  chapter  about  the 
soda  leaches  and  previous  to  the  description  of  the  pro- 
cesses and  expedients  for  the  recovery  of  the  soda,  it  may 
be  in  place  to  mention  that  the  name  "sulphaterstuff"  is 
really  not  correct,  as  the  sulphate,  e.g.,  the  sulphate  of 
sodium  does  not  exercise  the  dissolving  effect  on  the  in- 
crusting  constituents,  which  is  done  by  the  carbonate  of 
sodium  and  the  sulphide  of  sodium  while  in  the  prepara- 
tion of  the  leach  is  made  first  from  the  sulphate.  The 
soda,  which  may  also  be  produced  from  sulphate  of 
sodium,  made  by  the  cellulose  manufacturer  himself  by 
conversion.  Therefore  the  designation,  soda-cellulose, 
is  the  only  correct  one. 

For  this  purpose  formerly,  evaporating  furnaces  were 
principally  used,  like  those  employed  in  the  manu- 
facture of  soda.  In  Lunges  Handbook  of  the  manufacture 
of  soda  such  a  furnace  is  illustrated,  as  reproduced  in  fig- 
ures 18  and  19. 

In  this  illustration  g  is  the  pan  designed  for  'evapora- 
tion, which  is  deep  and  supported  by  stone  pillars,  so  that 


THE    MANUFACTURE    OP    CELLULOSE. 


35 


the  bottom  of  the  pan  is  exposed  in  order  to  facilitate 
cooling  off.  At  thie  left  is  the  grate  a  on  which  the  fire 
necessary  for  evaporation  is  maintained.  The  flames  first 
spread  over  the  fire-bridge,  kept  cool  by  the  waterpipe  c, 
then  over  the  calcining  sole  d,  over  the  somewhat  higher 
placed  sole  e,  and  finally  'over  the  evaporating  pan  g,  from 
where  they  are  let  into  the  fon  of  the  chimney.  The  solu- 
tion makes  its  way  oppositely  to  the  fire;  first  it  is  evaporat- 
ed in  the  pan,  until  solid  parts  separate  out,  then  the  mass 
is  drawn  out  on  the  side  upon  the  draining  sieve  i,  below 
which  the  solution  is  let  off  into  a  reservoir  and  from  there 


FIGURES  18   AND   19. 

by  means  of  a  pump  it  is  again  charged  into  the  pan,  to  be 
further  evaporated.  Through  the  funnel  f,  fixed  over  the 
first  calcining  sole,  the  solid  residus  are  filled  upon  it,  where 
the  last  of  the  water  evaporates  and  after  this  is  accom- 
plished, it  is  by  means  of  scrapers  drawn  into  the  compart- 
ment d,  and  there  calcined.  After  this  has  been  done  suf- 
ficiently, the  mass  consisting  of  carbonate  of  sodium  is  pull- 
ed out  from  the  chamber  d  at  its  side,  and  directly  into  iron 
wheelbarrows,  by  which  the  mass  is  again  carried  to  the  dis- 
solving tanks,  there  dissolved  and  made  caustic,  to  be  used 
again  in  boiling  wood. 


36  THE    MANUFACTURE    OP    CELLULOSE. 

Another  evaporating  furnace  was  constructed  by  Roeck- 
ner  in  Newcastle.  Here  the  leach  first  flows  into  a  cylin- 
drical vessel  lying  horizontally  and  is  there  concentrated 
by  boiling.  The  steam  therein  cooled  gets  into  a  conden- 
ser and  as  boiling  water  it  runs  into  a  reservoir.  The 
concentrated  leach  flows  through  a  pipe,  fixed  to  the  bot- 
tom of  the  vessel  in  an  open  pan  on  a  lower  level  where  it 
is  further  evaporated,  and  from  there  into  a  calcining  fur- 
nace, situated  below,  where  the  complete  conversion  into 
soda  takes  place.  From  there,  by  means  of  rakes,  the  mass 
is  pulled  into  the  cooling  chamber,  arranged  below.  Here 
a  current  of  air  passes  through  the  hot  mass,  assisting  the 
combustion  of  the  gases,  which  are  passed  into  the  fire- 
hearth  serving  the  other  parts.  By  this  the  odors,  which 
appear,  when  the  soda  is  simply  discharged  from  the  fur- 
nace and  brought  to  another  place  to  cool  off  are  avoided. 

To  obviate  the  considerable  wearing  out  of  the  expen- 
sive evaporating  pans,  with  the  present  evaporating  ap- 
paratus, Richard  Schneider  in  Dresden,  has  constructed 
an  evaporating  tower,  with  movable  drizzle  faces,  con- 
veniently adjustable  (D.  E.  P.  No.  34392),  which  may  "be 
employed  to  advantage  together  with  furnaces  for  the  re- 
generation of  soda.  This  furnace  consists, — the  plant  of 
the  gas  generator  and  the  chimney  not  considered,  (it  is  a 
regenerative  gas  furnace) — of  the  firebox  H,  in  which  the 
ignition  of  the  fuel  gases  takes  place  and  which,  accord- 
ing to  construction,  may  be  formed  so  that  it  may  give  off 
highly  heated  fire  gases  or  highly  heated  air  separate  from 
each  other  or  together.  Further  attached  to  the  single 
or  double  calcining  sole  C,  at  the  other  end  of  it,  set  out 
with  chamottstones  like  a  regenerator,  there  is  a,  short 
chamber  R,  which  during  the  calcining  process  isi  con- 
tributing substantially,  to  obtain  thorough  combustion  of 
all  gases  escaping  from  the  calcining  sole1,  and  thus  secur- 
ing smokeless  and  odorless  working.  Next  to  the  chamber 
R  is  situated  somewhat  higher,  a  quite  deep  tank  D,  serving 
as  inspiring  pan.  Over  D  thQ  evaporating  tower  E  is  erect- 
ed, with  its  movable  drizzle  faces^,  which  ought  to  have  a 
declination  of  less  than  30  degrees  against  the  horizon.  The 
number  of  the  drizzle  faces  depends  on  the  quantity  of 
solution  to  be  worked  per  unit  of  time. 

Above  C  and  R  there  are,  for  utilization  of  the  radiant 
heat,  a  large  tank  A,  from  which  the  smaller  tank  B,  put 


THE    MANUFACTURE    OF    CELLULOSE. 


37 


up  over  the  tower  E  is  being  fed  by  pulsometer.  The  space 
under  C  has  been  arranged  for  baking  and  cooling.  Into 
this  are  pulled  from  C,  through  correspondingly  construot- 
ed  doors,  with  which  C  is  provided,  the  red  hot,  but  not 
yet  deadbaked  masses,  which  under  this  system  do  not  need 
to  be  raked  out  in  front  of  the  furnace. 

The  products  of  combustion  of  part  of  the  fuel  gases, 


Fig.  20. 

charging  H,  are  carried  off  through  the  channel  s  to  the 
chimney  ;S.  The  part  of  the  channel  s  under  G  is  slight- 
ly vaulted,  or  still  better  covered  with  two  layers  of  thin 
chamotte  plates.  This  arrangement  and  construction  of 
s  is  for  the  purpose  of  utilizing  as  far  as  possible  the  heat 
of  passing  products  of  combustion  and  to*  keep  up  and  to 
quicken  the  calcining  process  of  the  masses  dropped  into 
G.  The  gases  thereby  evolved  (empyreumatic  gases),  are 


38  THE    MANUFACTURE    OF    CELLULOSE. 

by  special  channels  discharged  to  the  fire-hearth  and  there 
burned  up.  The  thoroughly  calcined  dead  masses  are 
then  at  regular  intervals  corresponding  to  the  different 
charges,  discharged  from  the  different  compartments  of  G 
through  the  doors  F  and  turned  over  to  further  manipula- 
tions. There  are  further  provided  at  m  adjustable  open- 
ings for  the  inlet  of  air,  and  at  d  for  the  inlet  of  the  fuel 
gas.  The  air  entering  at  m  gets  heated  along  the  vault 
over  C,  and  through  openings  n,  it  reaches  p,  there  to  eith- 
er cause  a  perfect  combustion  of  the  gases  coming  from  C 
or  to  burn  the1  gas  entering  by  d  to>  increase  at  times  the 
heat  in  D. 

The  leach  to  be  worked  is  first  run  into  the  tank  A, 
from  there  lifted  to  B  and,  drizzing  down  the  tower  in  the 
manner  described  above  and  giving  off  water  in  the  form 
of  vapor,  it  reaches  D,  from  where  in  a,  condensed  state  it 
is  charged  into  C,  where  it  is  finished.  The  fire-gases  com- 
ing from  H,  go  the  opposite  way,  as  with  other  evaporating 
furnaces.  The  arrangement  offers  the  a  Ivantage,  that  be- 
sides the  saving  of  a,  pan,  the  total  plant  ';akes  up  much  less 
space. 

Herr  Carl  Keller  had  previously  in  the  seventies,  built 
a  furnace  for  the  recovery  of  the  soda  from  straw-stuff 
leaches,  in  which  the  fire-gases  were  forced  by  means  of  a 
spray  of  superheated  steam  over  pans  arranged  like  shelves, 
one  above  the  other.  There  the  hearth  and  the  calciner 
were  under  draught,  while  the  back  part  of  the  furnace  and 
the  part  used  for  concentration  were  working  under  a 
slight  pressure  of  about  2  mm.  water  column.  This  ar- 
rangement permitted  the  fire-gases  to  be  led  slowly  over 
a,  large  evaporating  surface,  which  would  be  possible  only 
to  a  limited  degree  where  the  draught  of  a  chimney  alone 
was  defended  on,  owing  to  the  elastic  steam  formed  in 
evaporation. 

For  completeness  sake  it  may  be  mentioned,  that  an 
American  patent,  No.  388,284  by  John  F.  Kennedy,  is  in- 
tended to  make  use  of  the  heat  still  contained  in  the  cal- 
cined residues,  by  arranging  a  common  steam  boiler,  to 
produce  steam  by  their  radiant  heat.  Whether  this  ar- 
rangement, has  proved  a  radical  success,  is  not  known  to  the 
author. 

Another  arrangemnet  for  the  production  of  soda,  which 
has  proved  very  successful  in  practice,  is  in  operation  in 


THE    MANUFACTURE    OP    CELLULOSE,  39 

the  Cellulose  factory  Rannkem  in  Norway  and  is  described 
by  Herr  Laur.  W.  Yensen  in  No.  11  of  the  Papier  Zeitung, 
1889,  as  follows:  The  regeneration  of  the  salts,  contain- 
ed in  the  leaches  is  thus  accomplished  in  three  steps:  First, 
Evaporation  of  the  water  until  concentration  of  the  leach 
of  30  degrees  B  in  steam  boilers,  tubular  boilers  and  pans, 
whereby  the  fire-gases  are  so  led  against  the  opposite  direct- 
ed current  of  the  leach,  that  the  fire-gases  escaping  into 
4he  box  give  off  their  heat  until  as  low  as  150  to  200  °C. 
Second,  mspissation  of  the  concentrated  leaches  to  muddy 
consistency  by  open  fire  in  a  fire-proof  inspissation  pan. 
Third,  volatization  of  the  incrustings  while  melting  down 
the  salts  in  a  retort-iike  furnace,  which  is  so  connected  with 
the  inspissation  pan,  that  the  gases  enter  the  main  fire, 
there  being  burned  up  and  so  assisting  in  inspissating  the 
leach.  The  evaporation  starts  in  two>  steam,  boilers  A, 
which  are  connected  by  a  pipe  d;  the  solution  is  pumped, 
into  the  boiler  through  the  pipes  bb  and  remains  there, 
until  it  has  reached  a  certain  concentration.  The  steam 
evolved  in  the  boilers  is  in  the  domes  D  freed  from  the 
leach  carried  along,  by  arranging  in  each  of  them  a  sieve 
with  pieces  of  iron  thereon.  The  solution  concentrated  in 
the  boilers  is,  after  certain  intervals,  blown  off  through  the 
blow-out  pipe  g  and  then  through  the  pipe  line  h  is  run 
into  the  tubular  boiler  B. 

A  steam  pipe  r,  leads  the  steam  evolved  in  the  further 
evaporation  of  the  solution,  from  B  to  the  drying  cylinders 
of  the  paper  machine,  although  the  steam  may  be  used 
for  any  other  purpose.  The  heating  of  the  tubular  boiler 
is  done  with  the  steam  which  is  evolved  ir  the  evaporation 
of  the  solution  in  the  boiler  A,  and  which  gets  into  the 
heating  tubes  by  the  pipe  R?  from  the  dome  D.  Under  nor- 
mal conditions  the  solution  of  from  13  to  21  degrees  B  is 
evaporated  down  to  21  to  27  degrees  B  in  the  tubular 
boiler  and  then  run  off  into  the  highest  of  the  four  evapor-- 
ating  pans  C,  which  originally,  set  above  and  against  each 
other,  were  so  built  in  that  the  fire-gases,  which  were  strik- 
ing along  the  boiler  A  in  the  direction  of  the  arrows,  were 
now  passing  in  the  direction  of  the  arrows  over  the  lowest 
pan  and  further  on,  on  their  way  to  the  chimney,  over  the 
three  other  pans.  But  the  gases  got  cooled  off  too  much 
and  poor  draught  was  the  consequence;  besides,  the  space 
below  was  needed  for  a  smelting  furnace,  so  the  shelve  fur- 


40  THE    MANUFACTURE    OP    CELLULOSE. 

nace  was  taken  out,  and  the  gases  of  combustion  were 
passed  between  two  pans  filled  with  solution  directly  to 
the  chimney.  The  solution  is  thus  concentrated  down  to 
about  30  degrees  B  and  from  the  lowest  pan  through  a 
line  of  pipe  led  off  into  the  inspissating  tank  E.  The  in- 
spissating tan7i  is  a  low  vaulted  compartment,  lined  with 
lire-proof  material,  in  which  the  solution  stands  as  high 
as  the  upper  edge  of  the  fire-bridge.  The  plane-grate 
fire  hearth  F  produces  a  flame,  which  by  natural  draught 
strikes  into  the  tank  and  is  forced  by  the  vault  to  strike 
closely  along  the  solution,  whereby  the  water  is  further 
evaporated.  Through  openings  in  the  long  wall  of  the 
tank,  the  solution  is  continuously  stirred  while  inspissat- 
ing and  thus  its  dessication  is  furthered.  When  the  so- 
lution has  become  as  thick  as  heavy  mud,  the  fire  in  F  is 
dumped  and  the  mass  pulled -out  through  the  openings. 
It  is  then  thrown  into  the;  retort-like  smelting  furnace  LI, 
where  by  firing  in  the  box  N,  the  evaporation  of  the  re- 
maining water,  the  continued  combustion  of  the  incrusta- 
tions, and  the  melting  down  of  the  salts  takes  place.  The 
fire-gases  thus  make  their  way  as  follows :  The  gases  from 
L,  fig.  21,  mix  with  those  from  F,  strike  along  the  inspis- 
sating pan  E  and  mix  with  the  flames  of  the  smelting  fur- 
nace LI,  fig.  22.  The  hot  fire-gases  now  strike  along  both 
boilers,  from  back  to  front,  there  separate,  returning 
through  two  fire  canals  and  again  coming  together  strike 
over  the  pan  C.  The  fire-gases  are  on  their  way  deprived 
of  such  an  amount  of  heat,  that  they  escape  to  the  chim- 
ney with  a  temperature  not  higher  than  necessary  for  the 
maintenance  of  the  draught.  In  comparison  of  the  ar- 
rangements in  use  in  Europe,  the  one  in  question  offers 
considerable  saving  in  fuel,  by  thoroughly  utilizing  the 
fire-gases. 

With  1  kilo  of  coal  it  is  possible  to  recover  25  kilos  pure 
dessicated  salt  a.nd  yet  to  have  enough  steam  to  dry  15 
kilos  of  wood  fibre. 

The  same  Herr  Yensen,  who  has  accepted  for  years  the 
above  described  plant  as  satisfactory  in  practice,  much  pre- 
fers an  American  patent,  which  Homer  T.  Yargan  has  ob- 
tained for  a  process  of  regeneration  of  soda  and  which  is 
also  protected  in  Germany  by  patent  No.  42,592.  In  No. 
100,  Vol.  1888,  of  the  Papier  Zeitung,  this  device  is  de- 
scribed as  follows:  "Here  the  inspissation  is  not  effect- 


THE    MANUFACTURE    OP    CELLULOSE. 


41 


42 


THE    MANUFACTURE    OF    CELLULOSE. 


ed  by  direct  firing,  but  by  steam,  whereby,  it  is  claimed, 
the  expense  for  fuel  is  decreased.  Figs.  23  and  24  show 
the  arrangement  in  the  side  view  and  in  the  plane.  The 
concentration  is  carried  on  in  three  adjoining  cylinders. 
The  middle  parts  of  the  same,  H"  Hw  H"",  are  closed  by 
sectional  walls  against  the  extremities  L  I/  L",  and  A,  B, 
C.  The  extremities  are  connected  with  each  other  by  a 
number  of  narrow  pipes,  which  end  in  the  sectional  walls 
and  countersect  the  middle  parts.  The  spent  leach  to  be 
concentrated  is  forced  by  means  of  a  pump  through  the 
pipe  0',  run  into  the  cylinders  at  L  and  flows  through 
the  narrow  pipes  into  the  other  end  A.  Through  the  pipe 
K  steam  is  admitted  into  the  middle  part  H',  which  sur- 


Fig.  23, 

rounds  the  pipes  and  gives  off  its  heat  through  the  walls 
of  the  pipes  to  the  leach.  The  water  of  condensation  is 
continuously  let  off  through  the  pipe  V.  The  heated 
leach  runs  into  the  chamber  A,  gives  off  a  considerable 
quantity  of  steam  and  flows  in  a  thickened  condition  into 
the  chamber  E  below  A,  and  is  forced  through  pipe  U 
into  Li'  fig  24,  from  whence  again,  as  described  above,  it 
flows  through  narrow  pipes  to  the  end  of  the  cylinder  aft 

B,  and  from  there  through  pipe  U  into  L"  and  from  L"  into 

C.  The  steam  escaping  from  the  leach  in  the  cylinder  at  A, 
passes  through  pipe  H  into  the  second  middle  part  IT", 
and  here,  as  in  H"  the  live  steam  works  through  the  walls 
of  the  narrow  pipes  upon  the  leach.     The  water  of  con- 
densation is  again  carried  off  through  pipe  V.     The  steam 


THE    MANUFACTURE    OF    CELLULOSE. 


43 


escaping  from  the  leach  in  chamber  B  enters  through  the 
pipe  J  into 'the  third  middle  chamber  H"",  to  work  here 
in  the  same  manner,  as  stated  before.  The  steam  which 
continues  escaping  from  the  leach  in  the  chamber  C  is-, 
through  the  pipe  J,  drawn  into  the  condensator  W  of  the 
vacuum  pump,  while  the  concentrated  leach  is  carried  off 
by  the  pump  P. 

The  vacuum  produced  by  the  pump  0  acts  on  all  three 
cylinders  in  diminishing  degree,  so  that  in  the  chamber 
A  it  is  at  least  and  in  chamber  C  greatest. 

As  will  be  seen  from  the  above,  fresh  steam  is  let  only 
into  the  first  cylinder  H",  while  in  the  other,  evaporation 


Fig,  24. 

is  effected  by  the  waste  of  steam  of  the  leaches.  The  quan- 
tity of  steam  used  will  for  this  reason  be  small,  as  one 
triple-effect  Yargan  can,  for  instance,  evaporate  15  kilos 
of  water  with  1  kilo  of  coal.  The  leach  is  by  the  Yargan 
evaporator  concentrated  to  40  degrees  B;  the  whole  of  the 
soda-regeneration  is  far  cleaner  than  is  generally  found, 
besides  the  attendance  of  but  ten  men  altogether  is  neces- 
sary in  24  hours  to  recover  the  soda  for  twenty  tons  of 
wood  fibre,  while  in  the  Kankeim  apparatus,  for  instance, 
for  eight  tons,  twenty  men  were  needed.  The  Yargan  ap- 
paratus has  already  proved  eminently  successful  in  several 
American  factories.  In  one  of  them,  for  instance,  18  tons 


44  THE    MANUFACTURE    OP    CELLULOSE. 

of  coal  were  saved  per  day  as  compared  with  the  former 
method.  The  very  high  price  of  the  complete  plant  is,  at 
present  at  least,  a  drawback  to  its  more  extensive  introduc- 
tion in  Germany. 

Contrary  to  the  soda  process  just  described,  the  sul- 
phite process  is  based  on  treating  the  wood  with  acids,  and 
lately,  indeed,  with  sulphurous  acid  only,  consisting  in 
the  combination  of  one  part  of  sulphur  and  two  parts  of 
oxygen.  It  is  a  gas  of  strong  and  pungent  smell,  which 
mixed  with  air,  impedes  breathing,  but  is  not  so  absolutely 
injurious  to  the  human  system  as  one  would  think,  on  the 
contrary,  the  inhalation  of  the  gas,  properly  diluted  with 
air  and  with  due  precautions,  has  lately  been  recommended 
for  consumption,  and  is  for  this  purpose  already  employed 
practically,  for  instance  at  the  Augusta  Victoria  Bath  in 
Wiesbaden. 

At  low  temperature  or  high  pressure  the  sulphurous 
acid  gas  may  be  transformed  into  the  liquid  state.  Water 
absorbs  sulphurous  acid  gas  in  large  quantities,  as  water 
itself  is  also  attracted  by  it  from  the  air.  Upon  this  read- 
iness to  combine  with  water  depends  its  practical  employ- 
ment, because  an  aquous  solution  is  the  easiest  to  handle. 
The  American  Tilghman,  as  stated  in  the  chronological 
table  cited  at  the  beginning,  in  1866  first  recommended 
sulphurous  acid  for  dissolving"  the  incrustations,  and  he 
obtained  upon  a  process  embodying  this  feature,  the  Amer- 
ican patent  being  dated  October  26,  1867,  and  the  English 
March  31,  1867.  In  the  American  patent  the  entire 
method  of  manufacturing  is  very  exactly  and  copiously  de- 
scribed, while  the  Papier  Zeitung  in  1884,  the  later  prac- 
tical experiments  on  a  large  scale  are  described.  Notwith 
standing  the  fact  that  he  had  not  worked  out  his  inven- 
tion as  much  as  would  have  been  desirable,  he  turned  his 
energies  to  other  ideas,  so  that  the  promising  process  of 
producing  Cellulose  by  means  of  sulphite  solution  did  not 
rapidly  come  into  general  use.  Succeeding  Tilghman, 
Ekman,  in  Bergvik,  Sweden,  also  discovered  a  process  of 
producing  Celulose  by  sulphurous  acid  and  he  was  the  first 
one,  who  after  finishing  his  experiments,  made  on  a  large 
scale  a  product  fit  for  use,  he  first  manufacturing  secretly, 
and  did  not  take  out  a  patent  until  July  .13,  1881.  In 
Germany,  however,  he  was  preceded  by  Professor  Alex- 
ander Mitscherluch,  who  obtained  patents  not  only  on  the 


THE    MANUFACTURE    OF    CELLULOSE.  45 

chemical  process  of  producing  Cellulose  from  wood  by  sul- 
phite leach,  but  also  on  the  different  parts  of  the  neces- 
sary plant.  He  was  very  successful  in  making  a  great 
number  of  contracts  with  those  paper  manufacturers  who 
bought  of  him1  his  process  and  who  besides  obtained  the 
privilege  of  exclusive  rights  within  certain  territories.  In 
consequence  of  a  legal  suit,  the  principal  part  of  Mitscher- 
lich's  patent  No.  4,179  was  annulled  in  1884  by  the  Im- 
perial Court,  when  it  became  known  that  the  patent  of 
Tilghman  was  much  older.  Besides  this,  beginning  from 
the  year  1893,  a  vigorous  polemic  has  arisen  in  the  Papier 
Zeitung  as  to  whether  Mitscherlich  or  C.  D.  Ekman  had 
first  made  saleable  Cellulose  on  a  large  scale,  which  in  the 
end  was  decided  in  favor  of  the  latter.  Therefore  the  note 
contained  in  the  first  edition  of  this  book,  that  Professor 
Alexander  Mitscherlich  was  the  real  father  of  practical 
Cellulose  manufacture,  can  to-day  no  longer  be  completely 
sustained,  although  great  credit  is  due  him  on  account  of 
the  practical  execution  of  his  ideas  and  the  introduction 
in  business  of  the  process  named  after  him. 

We  will  first  consider  how  the  sulphite  leach  according 
to  Mitscherlich  is  made.  The  sulphurous  acid  is  produced 
by  burning  sulphur  or  compounds  containing  sulphur. 
Among  the  latter  is  the  comparatively  cheap  pyrite  which 
is  composed  of  about  nearly  one  part  of  sulphur  and  one 
part  of  iron.  When  sulphur  can  be  obtained  cheaply  i.  e.? 
cheaper  than  three  times  as  much  of  the  pyrite  would 
amount  to  one  would  decide  for  the  use  of  sulphur,  in  the 
combustion  of  which  a  direct  loss  can  hardly  happen,  while 
the  pyrite  after  roasting  shows  at  least  4$  unburned  sul- 
phur inside  the  different  pieces,  and  the  loss  sometimes 
reaches  10$.  In  using  solid  sulphur  the  furnace  may  be  of 
simple  construction.  A  chamber  of  mason  work,  the  bot- 
tom of  which  is  formed  by  a  heavy  iron  plate,  will  answer; 
some  low  iron  partitions  divide  the  combustion  chamber 
into  several  compartments,  every  one  of  which  is  accessible 
from  the  outside  through  doors,  so  that  filling  and  clean- 
ing can  be  done  alternately,  while  working.  The  furnace 
is  also  covered  over  with  an  iron  plate,  which  is  cooled  by 
water,  so  that  during  the  process  no  sulphur  can  escape  un- 
burned. The  controling  and  regulation  of  the  air  supply  is 
done  through  small  shutters  arranged  in  the  doors. 

Yery  often,  however,  pyrite  must  be  used  alone.     This 


46  THE    MANUFACTURE    OF    CELLULOSE. 

must  be  broken  into  pieces  with,  the  hammer  as  uniformly 
as  possible  of  about  the  size  of  a  nut.  There  are  stone 
breaking  machines  for  this  purpose,  but  they  are  supposed 
to  give  too  much  clear  waste  and  this  must  be  avoided. 
When  in  crushing  enough  of  the  fine  pyrite  has  accumu- 
lated, it  may  be  made  use  of  by  mixing  it  with  loam  and 
forming  into  small  balls,  which  after  being  thoroughly 
dried  on  the  furnace,  may  be  charged  into  the  furnace 
along  with  the  good  material,  without  danger  of  stopping 
the  grate.  It  should  be  mentioned  at  this  point,  that 
Herr  Maletra  has  constructed  a  plate-furnace,  which  is  em- 
ployed with  advantage  principally  for  roasting  fine  pyrite 
and  especially  dust. 

The  broken  pyrite  before  using  has  to  be  stored  in  a 
place  as  warm  and  dry  as  possible,  but  in  the  room  where 
the  furnace  stands*  Such  pyrite  furnace  is  illustrated  in 
figs.  25,  26  and  27.  The  furnace  is  almost  quadratic,  the 
inside  laid  out  with  Chamotte  brick,  about  1.5  meters  wide, 
spanned  over  by  a  flat  Chamotte  vault,  with  an  opening 
in  its  zenith  for  the  outlet  of  gases,  which  next  enter  a 
space  between  the  first  vault  and  another  one  spanned  over 
the  first  one.  Because,  as  a  rule  according  to  the  extent 
of  the  works,  three,  four,  or  more  pyrite  furnaces  are 
placed  side  by  side,  or  still  better,  with  their  backs  against 
each  other,  not  all  of  which,  however,  are  worked  at  the 
same  time,  they  must  be  connected  with  each  other  and 
with  the  different  towers  later  on  described.  This  is  done 
by  arranging  above  the  furnace  two  canals,  the  one  of 
which  is  by  the  opening  A,  the  other  by  the  opening  B 
connected  with  the  interspaces  mentioned.  Both  are 
closed  by  peculiarly  constructed  valves,  similar  to  water 
sealed  valves,  only  that  in  this  case  on  account  of  the  heat, 
not  water,  but  sand,  or  fine  pyrite  is  employed  as  a  means 
for  sealing.  The  second  vault  mentioned  also  serves  the 
purpose  of  protecting  the  inner  one  against  cooling  off. 
About  one-half  meter  from  the  floor  is  a  grate,  consisting 
of  single,  strong,  square  bars,  arranged  quite  close  togeth- 
er, which  by  means  of  a  key  fitted  to  the  front  end  can 
be  turned,  and  thus  during  roasting,  the 'cleaning  of  the 
grate,  i.  e.,  the  falling  through  of  the  slake  is  possible. 
The  front  opening  through  which  the  turning  of  the 
grate  bars  as  well  as  the  pulling  out  of  the  finished  pyrite 
is  performed,  and  likewise  the  fire  door  itself,  which  serves 


THE    MANUFACTURE    OF    CELLULOSE.  47 

for  the  feeding   of   fresh   pyrite   are   provided   with   well- 
fitting  doors,  which  as  a  rule  are  luted  besides  with  loam. 


1© 

s 
s 

I© 

k 

s 

^$s$s$^ 

l@ 

I© 

^ 
^ 

They  are  also  provided  with  a  small  hole,  closed  with  a 
shutter  or  glass  plate,  through  which  the  process  is  con- 


48  THE    MANUFACTURE    OF    CELLULOSE. 

struction  may  be  observed  at  any  time.  This  process  after 
the  furnace  has  once  been  started,  goes  on  in  the  following 
manner:  To  the  burning  pyrite,  kept  at  light  red  heat, 
enters  atmospheric  air,  the  oxygen  of  which  combines  with 
the  iron  from  oxide  of  iron,  and  with  the  sulphur  to  form 
sulphurdioxide  or  sulphurous  acid.  Hence  the  regulating 
has  to  be  managed  so  that  not  too  much  air  enters,  but 
enough  to  maintain  the  furnace  at  intense  red  heat.  Care 
must  also  be  taken  that  the  pieces  of  pyrite  all  get  thor- 
oughly burned  through,  so  that  only  iron  oxide  and  not 
part  of  the  sulphur  is  thrown  on  the  slake-pile,  what 
eventually  would  amount  to  considerable  loss.  Insufficient 
air  supply  has  besides  the  disadvantage,  that  sometimes 
separation  of  uncombined  sulphur  takes  place,  the  so-call- 
ed sublimation,  which  can  be  of  much  damage  in  the  later 
digesting  process.  In  order  to  obtain  in  the  next  manipu- 
lation a  most  concentrated  solution  of  sulphurous  acid,  the 
gases  leaving  the  pyrite  furnace,  must  contain  as  much 
sulphurous  acid  as  possible  and  this  can  be  only  when  the 
air  supply  is  limited  to  the  least  necessary  quantity,  when 
the  gases  themselves  possess  a  temperature  as  low  as  pos- 
ible.  Therefore  they  are  not  let  directly  into  the  tower, 
which  is  necessary  in  the  making  of  leaches  according  to 
the  system  of  Mitscherlich,  but  they  are  cooled  off  bv  lead- 
ing them  in  heavy  pipes,  up  to  about  two-thirds  or  three- 
quarters  of  the  height  and  down  again  to  the  foot  of  the 
tower.  For  this  reason  a  less  strong  solution  always  re- 
sults in  the  summer  months  than  in  winter,  which  must 
be  called  a  disadvantage  in  regard  to  uniform  working. 
This  may  be  somewhat  remedied  by  continuously  letting 
water  drizzle  down  the  outside  of  the  before  mentioned 
cooling  pipe,  though  this  is  far  less  effective  than  the  cold 
of  the  winter. 

What  influence  the  temperature  has  on  the  production 
of  the  leach  can  easily  be  seen  from  the  following"  little 
table,  showing  the  capacity  of  the  water  for  absorption  at 
different  degrees  of  temperature: 

Water  of  2°,  4°,  6°,  8°,  10°,  12°,  14°,  16°,  18° 
absorbs  75,  70,  65,  61,  57,  53,  49,  45,  42 

cubic  centimeters  of  sulphurous  acid  gas. 

At  the  above  mentioned  ascending  pipe,  near  the  fur- 
nace two  small  branches  (T's)  are  advantageously  arrang- 
ed, which  are  connected  by  a  glass  tube,  like  the  water- 


THE    MANUFACTURE    OF    CELLULOSE.  49 

indicator  on  steam  boilers,  so  that  the  circulation  of  the 
gases,  coming  from  the  pyrite  furnace,  can  be  observed. 
When  sublimation  has  taken  place  and  consequently  sul- 
phur is  untainted  in  the  gases,  a  yellow  coloration  will 
show  upon  the  glass  and  then  better  draft  must  at  once 
be  secured  i.  e.,  some  air  must  be  admitted.  To  transform 
the  gaseous  sulphurous  acid  into  the  aqueous  solution, 
mentioned  before,  it  is  necessary  to  lead  the  gas  against  a 
fine  shower  of  water;  the  aqueous  sulphurous  acid  so  ob- 
tained is,  however,  very  unevenly  composed  and  little  suit- 
ed for  the  subsequent  process  of  digesting.  For  this 
reason  it  is  preferred  to  use  combinations  with  bases,  which 
can  be  easily  stored,  and  for  practical  reasons  the  com- 
paratively chear)  lime-stone,  easily  obtainable  and  some- 
time also  magnesite,  were  chosen.  Mitscherlich  recom- 
mends lime  of  rather  porous  condition,  so  that  a  large  sur- 
face is  presented,  which,  however,  must  not  be  too  soft, 
as  it  would  then  dissolve  too  quickly,  become  muddy  and 
cause  clogging  of  the  tower.  The  lime-stone  is  broken  up 
into  pieces  of  about  100  m.  m.  diameter.  Other  factories, 
working  the  same  system,  do  not  use  tufa,  but  dolomite 
and  jura  lime,  and,  as  they  claim,  get  further  with  them,, 
on  account  of  their  greater  hardness.  Carl  Kellner  first 
used  dolomite  and  had  the  process  patented. 

The  tower,  which  is  tne  characteristic  sign  of  most  Cel- 
lulose works,  is  constructed  in  the  following  manner: 

Fig.  28  shows  an  outside  sketch  of  it,  and  fig.  29  the 
ground  plan.  Upon  a  strong  square  foundation  are  built 
two,  and  sometimes  four  or  more  reservoirs  of  masonary, 
open  at  the  top,  over  which  are  set  the  wooden  towers. 
These  towers  of  30  to  35  meters  in  height  are  formed  by 
setting  single  barrels,  properly  cylindrical  tubes  of  best 
resinous  pine,  bound  by  iron  hoops,  on  top  of  each  other, 
packing  the  joints  with  waste  and  coating  the  whole  heav- 
ily with  tar.  Because  the  lower  parts  ha,ve  to  stand  great 
pressure  on  account  of  the  lime  charge,  representing  ac- 
cording to  the  width  (as  a  rule  one  meter)  and  height  of 
the  tower  a  weight  of  over  1,000  C,  the  thickness  of  the 
lower  walls  must  be  made  heavier  and  also  the  number  of 
hoops  must  be  increased  where  the  dimensions  are  great- 
er. Directly  over  the  stone  reservoirs,  near  the  top  of 
which  the  gases  of  combustion  enter  from  the  pyrite  fur- 
naces and  at  the  bottom  of  which  the  finished  aqueous- 


50  THE    MANUFACTURE    OF    CELLULOSE. 

solution  is  let  into  the  leacli  reservoirs,  is  laid  a  heavy 
grate  of  oak,  the  single  beams  of  which  are  narrower  at 
the  tower  side.  That  the  great  weight  of  the  lime  shall 
not  rest  thereupon  alone,  two  other  heavy  beams  go  square 
through  the  tower,  being  supported  from  the  outside.  At 
the  upper  end  of  .each  tower  is  a  water  reservoir,  fed  from 
below  by  a  pump,  from  which  a  stream  of  water,  regulated, 
as  required  by  a  cock,  can  be  discharged  on,  the  lime.  It 
must  also  be  made  possible  by  means  of  a  valve  or  other- 
wise, to  let  a  larger  quantity  of  water  even  to  the  whole 
contents  of  the  reservoir  run  down  at  once,  when  it  be- 
comes necessary  to  rinse  cut  the  tower.  Close  below  the 
water  tank  is  a  side  opening  through  which  the  lime  is 
filled  in.  This  must  be  made  so  that  it  may  be  securely 
closed  and  there  must  also  be  some  smaller  openings  ar- 
ranged at  different  heights.  The  different  towers  are  sur- 
rounded and  held  together  by  a  strong  frame  work,  divided 
in  stories,  connected  by  stairs  and  roofed  over  on  top,  so 
the  whole  forms  a  single  ball  tower,  which  offering  a  large 
surface  to  the  wind,  must  certainly  be  well  anchored  to 
the  ground  by  wire  ropes.  In  the  uppermost  story  there 
is  generally  a  balcony  from  which  the  lime  buckets,  pre- 
viously hoisted  up  by  a  windlass,  are  carried  to  the  fill- 
hole.  Where  power  is  convenient  it  is  better  to  have  the 
hoisting  done  by  a  mechanical  elevator.  For  practical 
reasons  it  is  well  not  to  delay  the  first  filling  of  the  tower 
until  it  is  finished,  as  the  grate  suffers,  when  the  lumps  of 
lime  fall  from  so  high  a  distance;  the  lime  itself  gets 
crumbled  and  thus  in  the  beginning  might  cause  clogging, 
but  to  charge  the  different  sections  as  the  tower  is  build- 
ing up.  There  has  but  to  be  mentioned  that  the  ascend- 
ing iron  pipe  at  its  upper  end,  where  it  forms  the  ell,  is 
provided  with  a  cover,  which  must  be  well  luted.  This 
cover  is  opened,  when  a  newly  started  furnace  is  getting 
warmed  up  and  is  not  closed  until  the  pyrite  is  burning 
with  a  blue  flame,  and  the  charge  is  consequently  in  good 
order.  After  that  the  gaseous  sulphurous  acid  is 
permitted  to  enter  the  tower,  drawing  upwards  against  the 
water,  flowing  over  the  lime. 

Along  the  walls  of  the  tower  there  will  naturally  be 
large  spaces,  not  filled  out  with  lime,  also  the  water  will 
not  everywhere  evenly  wet  them  and  thus  the  upward 
drawn  sulphurous  acid  would  become  unequally  absorbed. 


THE    MANUFACTURE    OP    CELLULOSE.  51 


Fiff.    28. 


52  THE    MANUFACTURE    OP    CELLULOSE. 

To  prevent  this,  several  protruding  rings  are  fixed  to  the 
walls,  inside  of  the  tower,  against  which  the  gases  must 
strike  and  by  which  also  the  water,  which  might  otherwise 
run  down  the  walls  at  certain  places  only,  is  turned  off 
towards  the  centre  of  the  lime  charge.  By  the  contact  of 
the  sulphurous  acid  with  the  lime  taking  place  on  the  long 
run  through  the  tower,  sulphite  of  lime  is  next  formed,  where- 
by the  carbonic  acid  of  the  lime  is  set  free.  Then  the  sul- 
phurous acid  is  dissolved  by  the  water  and  this  again  dis- 
solves the  sulphite  of  lime,  which  is  soluble  in  water,  only 
with  difficulty,  and  thus  bisulphite  of  lime  is  formed.  As  al- 
ready mentioned,  the  temperature  is  of  great  importance 
in  the  chemical  process,  and  also  the  supply  of  air  in  the 
process  of  combustion;  this,  therefore  and  the  quantity  of 
water  running  down  must  always  be  taken  in  consideration, 
because  also  on  this  depends  the  concentration  of  the 
leach.  When  too  much  water  is  admitted,  the  resulting 
product,  the  aqeous  solution  of  bisulphite  of  lime,  would 
be  too  weak.  From  the  stone  reservoirs  in  the  foundation 
of  the  tower,  this  solution  is  now  let  off  through  a  lead  pipe 
int  large  wooden  tanks,  which  are  best  placed  so  high,  that 
afterwards  the  leach  can  be  run  through  a  line  of  pipes 
directly  into  the  digester.  Where  the  local  conditions  do 
not  permit  this,  it  is  best  to  use  a  reservoir  of  mason  work, 
well  covered,  from  which  the  leach,  when  needed,  can  be 
pumped  to  the  digesters.  In  this  case  it  is  advisable  to 
first  catchj  the  leach  in  a  barrel,  because  it  is  necessary 
during  the  concentration  of  the  leach  to  have  it  measured 
quite  often  with  the  areometer  by  the  man  employed  at  the 
pyrite  furnace,  and  also  by  the  technical  officials,  so  that 
when  the  leach  comes  too  weak,  the  fault  can  at  once  be 
remedied.  The  average  strength  is  4  1-2  to  5°  B  in  sum- 
mer, but  in  winter  7°  and  more. 

If  the  preparation  of  the  leach  has  gone  satisfactory,  the 
areometer  indicates  the  proper  strength  of  the  leach  in 
bisulphite  of  lime;  but  when  sublimation  has  taken  place, 
polythionic  acid  is  formed  in  the  tower  (according  to  D. 
Frank,  this  is  impossible)  the  compounds  of  which  are 
harmful  in  the  digesting  process,  while  in  the  leach  they 
are  estimated  wrongly  as  bisulphite  of  lime,  consequently 
the  concentration  is  measured  stronger  than  it  is  in  fact. 

In  this  pro'cess  there  has  repeatedly  occurred  a  clogging 
of  the  tower;  it  takes  place  after  one  or  two  days,  some- 


THE    MANUFACTURE    OP    CELLULOSE.  53 

times  oftener,  when  the  lime  partially  dissolved  by  the  acid 
and  washed  together  by  the  water  accumulates  below  on 
the  grate,  or  at  any  other  place,  and  renders  the  passing 
of  the  gases  impossible.  Draft  is  then  wanting  and  the 
furnaces  smoke,  i.  e.,  the  gases  come  out  at  the  joints.  The 
other  tower  must  then  be  put  to  work  at  once'.  The  im- 
pediment may  be  removed  by  opening  a  door  arranged 
directly  above  the  grate,  pulling  out  the  lowest  layer  of 
stones  and  rinsing  the  tower  once  or  several  times.  The 
same  result  may  be  achieved  by  causing  the  whole  lime 
charge  to  slide,  when  the  pieces  change  their  position  and 
the  working  order  is  restored.  As  soon  as  the  lime  charge 
in  the  tower  has  somewhat  settled,  new  lime  must  be  ad- 
ded. The  pieces  pulled  out  in  cleaning  the  tower,  if  not 
too  small,  and  after  being  well  rinsed,  may  be  mixed  with 
fresh  lime  and  filled  in  again. 

For  every  plant,  besides  the  towers  just  described,  anoth- 
er smaller  one,  a  so-called  "drive-over-tower,"  is  necessary, 
which  is  filled  with  the  waste  pieces  of  lime.  This  tower 
hias  a  smaller  diameter,  and  need  not  be  as  high  as  the  oth- 
ers. It  often  consists  of  kerosene  or  oil  barrels,,  set  one  above 
the  other.  In  the  sketch  in  fig.  29  it  is  marked  with  A.  It 
is  provided  with  grate  and  water  arrangement  like  the  oth- 
er tewers  and  is  only  used  when  an  operation  of  digesting 
has  been  finished  and  the  sulphurous  acid  gas,  under  pres- 
sure during  boiling,  must  be  blown  off.  The  digester  is 
connected  with  tlhe  small  tower  by  a  lead  pipe.  As  soon 
as  the  water  in  this  tower  has  arrived  at  the  lowest  part, 
the  blow-off  valve  of  the  boiler  is  opened;  the  gaseous  sul- 
phurous acid  rushes  against  the  water  and  as  long  as  the 
blowing  off  continues,  forms  a  strong  leach  of  about  12°, 
whichi  often  very  much  increases  the  concentration  of  the 
leach  already  in  the  basin. 

In  place  of  the  high  towers  recommended  bv  Mitscher- 
lich,  which  are  certainly  the  cause  of  many  inconveniences, 
but  which  must  be  high,  because  the  sulphurous  acid  re- 
quires much  time  to  decompose  the  carbonates  and  to 
transform  them  into  sulphites.  Later  on  two  towers  were 
recommended,  which  are  also  quite  satisfactory,  when  mag- 
nesite  is  used  instead  of  lime.  The  tower  need  then  to  be 
but  five  to  six  meters  high.  Erofessor  Hager  in  "Fabri- 
kation  des  Papiers,"  page  203,  writes  in  regard  to  this  as 
follows:  The  ball  towers  cause  a  multitude  of  discomforts 


54  THE    MANUFACTURE    OF    CELLULOSE. 

and  uncertainties  in  working,  not  only  because  of  the  hoist- 
ing of  the  raw  material  to  such  a  considerable  height,  but 
mainly  also  for  the  reason  that  on  account  of  the  great 
weight  the  lower  pieces,  already  become  softened,  get 
crumbled  and  render  difficult  the  ascent  of 
the  acid  gas.  Because  in  addition  to  this 
tall  towers  are  expensive  to  build  on  account  of  the 
foundation,  etc.,  it  has  been  recommended  to  build  in  place 
of  one  higfo  tower  several  low  ones,  for  instance  of  six  to 
eight  meters  high,  adjoining  each  other  and  connected  by 
pipe  lines  in  such  manner,  that  the  acid  not  absorbed  in 
one  tower,  is  caried  to  the  next  one,  and  so  on.  But  even 
this  arangement  has  its  disadvantages,  as  in  this  manner, 
if  the  most  careful  regulation  of  the  water  supply  is  not 
absorbed,  sulphite  solutions  of  much  varying  concentra- 
tion are  obtained,  because  in  the  last  tower  but  little  acid 
is  left  for  absorption.  But  as  time  for  action  can  be  pro- 
cured for  the  gas  by  giving  great  square  dimensions  to  the 
tower,  it  seems  well  considered  to  employ,  instead  of  tall 
and  narrow  towers,  low  and  wide  ones  of  a  shape  deviating 
from  the  cylindrical;  especially  when  it  is  considered  that 
a  saturated  sulphite  solution  is  best  obtained  by  successive 
strengthening  up,  and  by  the  meeting  of  unweakened  gas 
with  the  sulphite,  immediately  before  leaving  the  tower. 
For  this  purpose,  at  the  point,  where  the  gas  first  comes 
in  contact  with  the  material,  the  tower  should  not  be  wide, 
but  above  this  point  it  should  gradually  become  wider  to 
give  the  gas  much  time  for  action,  and  should  then  become 
narrow  again  towards  the  top,  to  increase  the  velocity  of 
the  gas  in  proportion  to  its  decreasing  strength. 

The  tower  built  on  this  principle,  illustrated  by  fig.  30 
consists  of  two  cones,  the  lower  one  inverted  so  that  they 
are  joined  at  their  greatest  diameter,  which  construction 
offers  the  advantage  that  with  less  height 
a  considerable  charge  is  possible  while  the 
walls  of  the  lower  cone  form  a  support  for  the 
raw  material,  which  now  settles  down  as  it  gets  dissolved, 
without  danger  of  clogging  of  the  drain-holes,  which  are 
arranged  at  b,  and  which  widen  towards  the  lower  side.  In 
such  manner,  with  a  tower  of  but  about  7  meters  total 
height,  a  capacity  of  7.5  cubic  meters  is  gained,  when  the 
dimensions  in  the  proportion  as  given  in  the  sketch,  are 
followed.  In  the  sketch  can  also  be  seen  the  inlet  pipe  for 


THE    MANUFACTURE    OF    CELLULOSE.  55 

the  gases  at  a,  the  reticulate  vault  at  b,  the  opening  at  c, 
for  the  charging  of  the  raw  material,  which  can  be  closely 
shut  by  an  asphalted  or  annealed  iron  plate,  the  outlet  pipe 
for  the  gases  at  d,  and  the  sprinkling  arrangement  at  e, 
with  the  water  supply  pipe  at  r.  The  vessel  A  into  which 
the  sulphite  solution  is  running  from  0,  is  practically  ar- 
ranged in  the  vault  G,  outside  of  the  axis  of  the  tower,  so 
that  by  removing  the  coverD,  it  can  be  cleaned  of  the  un- 
dissolved  particles  of  earth  carried  along  and  accumulating 
there.  The  emptying  is  either  done  through  a  lead  pipe, 


Fier.    30. 

with  a  stop,  or  by  a  lead  syphon.  It  is  necesary  to  take 
care  that  the  gas  is  completely  absorbed  on  account  of  its 
damaging  influence  on  vegetation  and  to  let  the  air,  com- 
ing from  the  tower,  before  it  escapes  into  the  atmosphere, 
pass  through  a  mass,  which  absorbs  the  rest  of  the  acid. 
For  this  purpose  milk  of  lime  or  a  soda  solution  is  used; 
which  is  conformingly  kept  in  a  vessel  placed  at  f,  which 
can  be  hermetrically  closed.  Into  this  the  air  from  the 
tower  enters  through  the  pipe  r,  and  after  circulating 
through  the  solution  leaves  through  the  pipe  g.  After  the 


56  THE    MANUFACTURE    OF    CELLULOSE. 

solution  has  become  saturated,  it  can  be  directly  let  through 
pipe  r  into  the  tower,  when  making  sulphite  of  lime.  But 
if  soda  lye  is  contained  in  tank  f,  the  sodium  sulphite  ob- 
tained is  filled  into  glass  vessels  to  be  used  as  antichlor. 
To  prevent  damaging  the  inside  lead  lining  of  the  tower, 
which  is  easily  done  when  filling  in  the  raw  material,  it  is 
advisable  to  cover  the  lower  cone  with  wooden  slats,  which 
also  form  gutters,  p^rmittin^  the  sulphite  solution  to  run 
off.  It  will  answer,  however,  if  instead  of  this  arrange- 
ment the  walls  of  the  tower  are  protected  by  a  coating  of 
tar  or  asphalt.  Whether  practical  experiments  have  been 
made  according  to  this  proposition  is  not  known  to  the 
author. 

Another  method  for  the  preparaton  of  sulphite  leach,  in 
which,  however,  the  tower  system  is  also  employed,  is  the 
one  according  to  the  process  of  Ritter-Kellner.  Herr 
Kellner  has,  according  to  his  own  personal  statement,  by 
accident  indeed,  but  independent  of  Mitscherlich,  discov- 
ered the  most  profitable  application  of  sulphurous  acid  :n 
the  manufacture  of  cellulose,  and  so  perfected  it,  that  at 
present  a  greater  number  of  the  cellulose  manufacturers 
work  according  to  his  instructions  (whidh,  however,  have 
been  amended  by  some  in  many  directions)  and  manufac- 
ture a  product,  which  in  certain  respects  indeed  differs 
from  Mitscherlich  cellulose,  but  which  is  excellent. 

In  Hover's  work,  page  214,  the  schematic  drawing  of 
this  system,,  as  taken  from  the  French  patent  No.  157,754, 
is  illustrated,  as  far  as  the  leach  making  is  concerned,  and 
the  following  description  is  given:  The  making  up  of  the 
sulphite  is  carried  on  in  a  circular  run,  beginning  with  the 
solution  of  the  sulphite  of  lime  in  weak  sulphuric  acid,  un- 
tainted in  the  tank  A,  running  into  tank  D  through  pipe  a, 
and  on  its  way  passing  an  injector  at  B,  to  draw  along  sul- 
phurous acid  gas,  purified  and  cooled,  through  the  pipe  R, 
connected  with  the  sulp'hur  burner  and  thus  saturated 
reaching  tank  D,  charged  with  lime  stone.  In  this  tank 
is  a  false  bottom,  below  which  the  sulphite  solution  accum- 
mulates,  which  by  a  pump  P,  is  forced  up  into  tank  A,  and 
kept  in  circulation,  until  it  has  reached  the  proper  strength, 
to  be  then  let  off  through  the  leaden  faucet  h.  The  car- 
bonic acid  liberated  from  the  carbonate  of  lime  in  D,  and 
the  unabsorbed  sulphurous  acid  and  finally  the  air,  coming 
from  the  sulphur  and  pyrite  furnaces,  reach  partially  the 


THE    MANUFACTURE    OP    CELLULOSE. 


57 


water  tank  G,  through  the  pipe  R",  and  its  branch  R",  and 
partially  enter  again  into  circulation,  drawn  up  by  the  in- 
jector B  through  pipe  R.  As  the  end  n  of  pipe  R",  is  per- 
forated and  laying  in  the  water  tank  C,  the  rest  of  the  sul- 
phurous acid  is  absorbed  by  the*  water,  while  air  and  car- 
bonic a,cid  go  off  free.  The  water  contained  in  C  is  then 
through  the  pipe  b,  provided  with  a  valve  for  regulating  and 
the  injector  pipe  a  carried  to  the  absorption  apparatus  and 
used  to  dissolve  the  sulphite.  According  to  another  ar- 


Fig.  31. 

rangement  (fig.  32)  towers  are  also  used  and  in  such  man- 
ner, that  the  sulphurous  acid  gas  is  drawn  from  the  furnace 
by  a  steam  injector  and  first  carried  to  a  large  low  horizontal 
chamber  A,  to  get  rid  there  of  the  dust  carried  along  and  to 
cool  off,  to  which  purpose  the  chamber  is  provided  with 
partition  walls,  forming  a  labyrinth  and  covered  by  a  tank 
B,  in  which  is  cold  water.  Then  the  gas  passes  through  a 
coil  C  and  enters  in  the  ordinary  way,  into  common  towers 
I  and  II,  filled  with  lime  stone.  Above  the  first  tower  I  there 
is  a  tank  D,  into  which  is  pumped  from  E  the  weak  sul- 


58 


THE    MANUFACTURE    OP    CELLULOSE. 


phite  solution,  obtained  in  the  tower  II  and  run  into  tank 
E,  to  be  thus  repeatedly  exposed  to  the  gas,  by  drizzling 
dlown  this  tower  instead  of  water.  But  over  the  second 
tower  a  water  reservoir  F,  is  arranged,  from  which  a  shower 
of  water  runs  down  the  tower  II.  To  bring  into  circula- 
tion again  the  sulphurous  acid  not  absorbed  in  the  tower  I, 
there  is  a  connection  made  between  both  towers  by  a  pipe 
r,  through  which  the  gas  accumulated  in  the  upper  space  of 


P 


tower  I  gets  into  the  lower  part  of  tower  II.  Through  the 
pipe  s  the  concentrated  solution  flows  into  cisterns,  and 
through  pipe  t,  carbonic  acid,  air,  etc.,  enter  the  open  at- 
mosphere. 

One  can  see  from  the  description,  that  the  preparation  of 


THE    MANUFACTURE    OF    CELLULOSE.  5» 

leach,  according  to  this  system,  is  much  similar  to  the 
Mitscherlich  system,  but  in  some  respects  appears  much 
more  rational,  because  by  connecting  two  towers  (which  do 
not  need  to  be  very  high)  and  arranging  some  pipes,  be- 
sides pump  and  injector,  a  circulation  is  produced,  by 
means  of  which  a  more  equal  concentration  of  the  leach 
can  be  obtained,  more  easily  and  safely,  which  in  regard  to 
the  subsequent  process  of  digestion,  must  be  considered  an 
advantage. 

Since  the  appearance  of  the  first  edition  of  this  book  the 
author  has  by  personal  observation  in  factories  in  Saxony 
and  Bohemia,  become  extensively  acquainted  with  the  sul- 
phite process  according  to  Ritter-Kellner. 

The  leach  plant,  according  to  Kellner,  as  carried  out  in 
practice,  is  illustrated  in  fig.  33  and  34,  as  contained  in  set 
1894,  page  2,683,  of  the  Papier  Zeiting.  This  plant  repre- 
sented on  a  scale  of  1:200,  consists  of  two  or  more  wooden 
towers  or  saturation  tubes  I  and  II,  built  vertically  one  next 
to  the  other,  which  are  connected  by  the  stone  waf&  pipe  S. 

The  filling  material  rests  on  grates,  A  in  fig.  33,  and  is 
to  be  selected  according  to  the  nature  of  combinations  to 
be  made.  It  is  recommended  in  the  Kellner  method,  to 
fill  the  towers  either  with  Dolomite  in  order  to  produce  a 
doublesalt  of  acid-sulphite  lime-magnesia  or  with  carbon- 
ate of  lime  to  make  lime  bisulphite. 

Above  these  towers  are  the  tanks  Tl  and  T2,  of  which  Tl 
is  filled  with  fresh  water  and  T2  with  the  solution  from 
tower  I.  The  outlet  from  these  tanks  into  the  overflow 
cups  U  below  is  regulated  by  an  arrangement  adjustable 
from  below.  The  overflow  cups  also  serve  to  distribute 
the  sprinkling  of  the  pieces  of  lime  uniformly  and  offer 
the  advantage  that  they  do  not  easily  get  clogged  up  like 
sprays  and  distributing  pipes.  Ml  and  M2  are  vessels  of 
brass  in  which  the  concentration  and  quality  of  the  solu- 
tions running  out  of  the  towers  I  and  II  are  measured. 

The  sulphurous  acid  gas,  coming  from  the  sulphur  acid 
pyrite  furnaces  runs  in  the  direction  of  the  arrows  through 
the  sublimatory  K,  and  is  drawn  off  by  the  injector  D 
and  blown  through  the  cooling  pipes  Dl.  These  are  laid  in 
a  cistern,  into  which  water  is  flowing  from  pipe  1.  At 
the  other  end  just  as  much  water  is  running  off  through 
the  canal  11.  The  well  cooled  gases  then  enter  the  tower 


60  THE    MANUFACTURE    OF    CELLULOSE. 

I  from  below  up  to  El,  spread  along  the  stones  in  there, 
sprinkled  with  water  from  above,  find  their  exit  above  at 
E2,  a  mixture  of  sulphurous  acid  gas,  carbonic  acid,  nitro- 
gen and  air  and  are  carried  downwards  through  the  stone- 
ware pipe  S,  until  at  E3  they  enter  the  tower  II  there  to  as- 


cend again  and  to  be  completely  absorbed.  The  unabsorb- 
ed  gases,  like  nitrogen  carbonic  acid  and  air  escape  through 
pipe  C  into  the  open  air. 

The  sublimatory  K  is  a  low  tower,  tightly  closed,  by  a 
partition  divided  into  two  chambers.  These  chambers  are 
filled  with  non-corrosive  material,  like  pieces  of  brick, 
basalt  stone  or  cake,  which  rest  on  grates  and  offer  a  large 


THE    MANUFACTURE    OF    CELLULOSE. 


61 


surface  to  the  sulphurous  acid  gas  passing  through  for  the 
disposition   of  the  sublimed   sulphur.     In  the  wall  trap 


doors  and  others  for  cleaning  are  provided  and  it  is  of 


62  THE    MANUFACTURE    OF    CELLULOSE. 

advantage  to  have  the  covers  consist  of  pans,  which  are 
cooled  with  water  circulating  through  and  cool  off  the  gas 
passing  through  the  chamber. 

While  the  gases  are  circulating  as  described,  water  is  let 
into  the  tower  II  from  above,  i.  e.,  opposite  the  entering 
of  the  gases.  It  sprinkles  the  limestones,  leaves  the  tower 
at  r2  and  runs  as  weak  solution  through  pipe  r2  and  meas- 
uring vessel  M2  into  the  tank  E2;  from  this  it  is  forced 
by  the  pump  P  into  the  upper  tank  T  of  tower  I,  from  there 
it  runs  into  the  tower  sprinkling  its  charge  and  leaves  it, 
as  finished  leach,  to  run  off  through  pipe  rl  and  measur- 
ing vessel  Ml  into  the  tank  E.  A  second  pump  PI  forces 
the  leach  from  there  to  the  digesters. 

Later  Henry  Kellner  designed  and  installed  several 
other  methods  of  preparing  leach.  In  a  large  German 
factory  for  instance  he  draws  the  sulphurous  acid  from  the 
pyrite  furnaces,  forces  it  through  a  wash  vessel  and 
then  through  four  wooden  tanks,  placed  one  above  the 
other,  in  which  are  limestones  and  which  are  filled  with 
water,  which,  following  the  law  of  gravitation,  flows  from 
one  tank  into  the  other  and  runs  off  below  as  finshed  leach. 
On  page  2,714  set  1894  of  the  Papier  Zeitung  is  described 
and  in  fig.  35  and  36  are  here  illustrated,  such  a  battery  of 
tanks,  as  working  advantageously  in  Waldorf  near  Mann- 
heim, the  largest  cellulose  works  of  the  world.  This  tank 
method  depends  on  absorption  of  the  masses  and  consists 
in  forcing  the  purified  and  cooled  gases  by  a  compressor 
through  the  tanks,  containing  water  and  limestone.  The 
solution  runs  from  one  tank  into  the  other.  The  tanks 
I  to  V  are  so  arranged  that  the  solution  therein  contained 
can,  through  the  connecting  pipes  w2  and  w5,  provided 
with  valves,  flow  into  the  next  one,  until  reaching  V.  The 
water  flows  through  pipe  Wl  into  tank  I,  which  like  II,  111 
and  IV  is  provided  with  a  perforated  .false  bottom  on  which 
the  limestone  charge  rests.  The  sulphurous  acid  gas  com- 
ing from  the  compressor,  consequently  under  pressure  en- 
ters through  pipe  g,  into  the  lowest  tank  V,  which  receives 
the  solution  from  tank  IV,  but  does  not  have  a,  false  bot- 
tom nor  a  limestone  charge.  The  acid  not  absorbed  by 
this  solution  goes  through  the  lead  pipe  g5  into  the  coil 
under  the  false  bottom  of  tank  IV  through  the  openings 
of  which  it  is  evenly  distributed  over  the  tank.  Likewise, 
the  unabsorbed  acid  goes  through  pipes  g4,  g3,  g2  until 


THE    MANUFACTURE    OF    CELLULOSE. 


63 


reaching  tank  I,  from  where  any  remaining  gas  is  again 
carried  off  through  pipe  gl.     The  gas  pipes,  g5  and  g4, 


.9s 


Figures  35  and  36. 
are  carried  as  high  as  shown  in  the  sketch,  in  order  that 


64  THE    MANUFACTURE    OF    CELLULOSE. 

no  liquids  from  the  higher  tanks  can  run  into  the  lower 
ones.  When  the  plant  is  managed  rightly  nothing  but 
air  devoid  of  acid,  should  leave  here,  as  it  should  te  ab- 
sorbed by  the  liquid,  through  which  it  is  circulated.  The 
solution  arriving  in  V,  there  takes  up  sulphurous  acid  only, 
but  no  lime,  and  runs  off  through  the  leach  measure  P. 
Each  tank  is  provided  with  a  manhole  of  hard  lead  and 
a  gauge  glass.  Stairs  facilitate  the  access  to  all  parts. 

In  American  factories  he  has  further  introduced  a 
method  by  which  in  low  absorption  towers,  connected  with 
each  other  counter-current,  aqueous  sulphurous  acid  is 
first  prepared,  which  is  then  saturated  with  the  desired 
quantity  of  the  base  in  tanks  filled  with  limestone,  and 
methodically  connected  in  series. 

The  importance  which  D.  Kellner.  has  from  the  start 
paid  to  the  proper  cooling  of  the  sulphurous  acid  gas  from 
the  furnace,  may  be  inferred  from  the  dimensions,  which 
he  gave  to  the  respective  cooling  arrangements.  The  man- 
ager of  one  of  the  oldest  Bohemian  factories,  planned  after 
his  system  made  to  the  author  the  concerning  statement 
that  Kellner  had  recommended  a  system  of  pipes,  14  me- 
ters long  and  3  meters  wide,  presenting  a  cooling  surface  of 
from  55  to  60  square  meters.  Besides,  when  these  cooled 
gases  are  drawn  by  means  of  a  pump  through  the  one  or 
several  towers  thereby  rendering  the  saturating  of  the 
water  entirely  independent  of  the  draft  in  the  tower,  the 
formation  of  the  leach  becomes  much  more  uniform  than 
is  possible  in  the  Mitscherlich  process. 

In  connection  with  this  it  may  be  mentioned  that  some 
factories,  and  especially  those  working  the  Kitter-Kellner 
system,  use  commercial  liquid  sulphurous  acid,  either  ex- 
clusively or  as  a  reserve,  for  convenience  or  uniformity. 
This  is  stored  in  a  strong  vessel,  provided  with  pressure 
gauge  and  gauge  glass,  and  can  be  used  any  time,  either 
directly  or  to  improve  the  leach  from  the  tower,  when  it  is 
too  weak.  In  most  instances,  however,  the  liquid  sulphur- 
ous acid  comes  too  high  and  besides  much  care  has  to  be 
observed  in  transportation  during  summer,  because  direct 
sunlight  may  cause  so  much  heating  and  also  evaporation 
of  the  sulphurous  acid  that  there  is  danger  of  explosion. 
The  accident  in  the  cellulose  factory  in  Ober-heschen,  some 
years  ago,  should  be  a  warning.  Sometimes  it  is  com- 


THE    MANUFACTURE    OF    CELLULOSE.  65 

plained  that  much  sulphuric  acid  is  still  contained  in  the 
liquid  sulphurous  acid. 

Lately  Dr.  Kellner  has  recommended  still  another  dis- 
solving method,  i.  e.,  to  employ  gaseous  chemicals  instead 
of  liquid  leaches.  In  the  Papier  Zeitung  the  following 
statement  has  been  made  by  him:  Until  recently  the  veg- 
etable materials  used  for  the  manufacture  of  cellulose  were 
treated  with  liquids  suitable  to  dissolve  and  decompose  its 
incrusting  constituents.  This  has  the  disadvantage,  that 
a  very  large  quantity  of  the  liquid  chemicals,  as  well  as 
their  employment  under  pressure  or  high  temperature  is 
necessary.  The  present  invention  concerns  a  method  by 
which  the  production  of  cellulose  can  be  attained  with 
much  less  expense  in  chemicals  and  without  the  application 
of  pressure  or  high  temperature  (except  in  some  cases, 
where  the  structure  of  the  plants  is  especially  dense);  re- 
sulting in  considerable  saving  and  besides  a  much  less 
weaker  end  product. 

This  process  is  characteristic  in  this,  that  the  chemicals 
which  are  to  decompose  the  incrusting  substance  of  the 
vegetable  materials,  are  brought  in  contact  with  them  in 
gaseous  condition.  For  this  purpose  all  those  chem- 
icals, are  suitable  which  exercise  upon  the  incrusting  sub- 
stance a  hydrolytic  or  oxydizing  influence,  especially  nitro- 
gen-oxide, nitrous-acid,  nitrogen,peroxide  and  chlorous 
acid.  In  working  this  process,  the  more  or  less  dry  veg- 
etable materials  are  if  necessary  previously  steamed  and  ex- 
posed to  the  action  of  these  chemicals  in  vessels,  made  re- 
sistant to  the  gases  and  vapors  mentioned. 

The  vegetable  material  treated  in  this  manner  is  then,  ac- 
cording to  the  kind  and  quality,  worked  with  cold  water  or 
steamed,  or  else  put  under  mechanical  treatment  (in  mills, 
etc.  ),afterwhich  they  are  treated  with  an  alkaline  solution  in 
order  to  dissolve  in  the  alkalies  the  incrusting  substances  pre- 
viously decomposed  by  the  gases  and  vapors.  The  so  treat- 
ed vegetable  material  is  then  violently  agitated  by  ma- 
chines such  as  are  used  in  the  paper  industry,  in  order  to 
get  the  cells  laid  free  by  the  treatment,  out  of  their  par- 
allel position.  After  this  the  produced  cellulose  is  washed 
and  if  necessary,  bleached. 

It  is  of  special  advantage  to  expose  the  vegetable  mate- 
rial treated  with  the  gaseous  and  vaporous  and  gaseous 
oxidizing  means,  after  washing  with  water,  to  the  action 


66  THE    MANUFACTURE    OF    CELLULOSE. 

of  ammonic  vapors,  because  the  ammonia  can  easily  be 
recovered  in  a  pure  state  of  heat.  With  some  kinds  of 
wood,  carbonate  of  soda  or  caustic  soda  must  be  used  to  dis- 
solve the  incrusting  substances;  in  such  case  the  alkaline 
solution  is  advantageously  added  at  the  same  time,  when 
worked  in  the  roll  or  stamping  mill,  because  using  the  lat- 
ter requires  but  a  small  quantity  of  the  alkaline  solution 
and  it  is  quickly  distributed  through  the  vegetable  mate- 
rial. 

To  avoid  the  repeatedly  mentioned  disadvantages  of  the 
towers  and  to  be  able  to  use  with  more  convenience  the 
burned  lime,  which  combines  more  readily  with  sulphurous 
acid,  a  number  of  vessels  filled  with  milk  of  lime,  were  put 
in  use  and  thus  the  so  called  chamber  apparatus  was 
formed.  The  chambers  of  mason  work,  closed  on  top,  are 
to  three-quarter  of  their  height  filled  with  milk  of  lime, 
through  which  the  gas,  coming  from  the  furnace,  has  to 
pass.  To  this  purpose  partition  walls  go  from  the  top 
down  near  to  the  bottom  so  that  in  every  chamber  the 
sulphurous  acid  gas  is  forced  to  pass  downwards  through 
the  milk  of  lime  and  to  rise  up  again.  Because  by  itself 
this  would  not  go  on  quickly  enough,  a  ventilator  is  used 
as  a  rule,  which  is  placed  behind  the  last  chamber,  caus- 
mg  a  draft.  In  the  same  place  an  injector  is  often  used,  or 
a  chimney  to  create  the  necessary  draft.  This  chamber 
system  has  been  brought  to  the  greatest  perfection  by  W. 
Flodquist  in  Gothenburg,  who  has  placed  10  chambers  in 
a  series  so  arranged  that  the  solution  is  circulating  through 
the  chambers  until  it  possesses  the  required  strength  of 
5°B. 

A  method  quite  similar  to  the  chamber  system  has  been 
patented  by  the  Englishman,  Dougall.  The  American 
patent  No.  311,595  was  described  in  the  Papier  Zeitung, 
with  illustrations,  represented  in  fig.  37:  The  process  con- 
sists in  burning  sulphurous  or  pyrite  in  strong  retorts,  into 
which,  after  the  sulphur  has  started  burning,  compressed 
air  is  introduced  by  means  of  a  powerful  blower.  The 
sulphurous  acid  thereby  produced  is  by  a  system  of  pipes 
let  into  a  number  of  vessels,  which  are  filled  with  water 
or  alkaline  solution.  In  these  vessels  the  gases  are  brought 
in  contact  with  the  liquid  and  the  absorption  so  effected. 
Instead  of  this  arrangement  an  exhaustor  may  be'  used  at 
the  opposite  end,  which  draws  the  air  through  the  retorts, 


THE    MANUFACTURE    OF    CELLULOSE.  67 

In  every  case,  the  temperature  of  the  retorts  is  kept  as  low 
as  possible,  so  that  few  gases  can  escape.     For  this  pur- 


pose, the  retorts  in  which  the  burning  of  the  sulphur  is  af- 


68  THE    MANUFACTURE    OP    CELLULOSE. 

fee  ted,  are  surrounded  by  a  water  jacket.  The  pipe  sys- 
tem, carrying  the  gas  to  the  saturation  tanks,  is  also  pro- 
vided with  a  water  cooling  device.  The  sulphurous  acid 
gas  is  entering  into  the  tanks  directly  below  the  water 
level.  These  tanks  are  provided  with  stirring  arrangement. 
By  the  aid  of  this  explanation  the  different  parts  of  the 
plant  can  be  easily  found  in  the  sketch.  A  is  the  blower, 
which  drives  the  air  through  the  retort  B.  After  the  sul- 
phur inside  the  retort  has  been  lighted  with  a  hot  iron,  it 
receives  a  liberal  air  supply  from  the  blower,  and  the  com- 
bustion goes  on  at  once  without  being  further  assisted  by 
outside  heat.  Overheating,  which  would  be  detrimental  to 
the  process,  is  prevented  by  the  water  jacket  Bl.  The  pipes 
next  connecting  to  the  retort  B  are  also  provided  with  a 
water  jacket,  Bl.  The  pipe  C  then  carries  the  gas  to  the 
tank  E,  in  which  the  stirrers  H,  are  arranged,  so  that  the 
liquid  comes  in  close  contact  with  the  gases. 

A  number  of  such  tanks  E  communicate  by  the  valves 
SI,  S2,  S3  etc.  As  long  as  the  circulation  of  the  gases  is 
going  on  these  valves  are  closed.  The  water  or  the  dis- 
solving agent  is  filled  in  the  last  tank  through  the  pipe  F. 
Before  the  gas  is  blown  in,  the  tanks  are  filled  through  the 
valves  S,  so  high  that  the  pipes  B  are  considerably  below 
the  level  and  the  gas  is  driven  right  into  the  liquid.  The 
gas  in  excess  is  carried  off  from  the  last  tank  through  the 
pipe  D.  To  control  the  height  of  the  liquid  in  each  tank 
and  for  the  taking  of  samples,  glass  tubes  GG,  with  cocks 
are  provided.  The  work  proceeds  in  the  manner,  that  the 
gas  is  driven  through  the  tanks  until  the  solution  in  the 
first  tank  has  reached  the  desired  point  of  saturation.  The 
blowing  is  then  stopped,  the  liquid  is  run  off  from  the  first 
tank  and  by  opening  the  valves  S£,  S3  and  F,  it  is  filled  up 
to  its  former  level.  The  blowing  is  then  started  again  and 
continued  until  a  solution  of  the  required  strength  is  again 
obtained  in  the  first  tank.  The  number  of  the  tanks  must 
be  made  large  enough  so  that  through  the  pipe  D  but  a 
small  excess  of  sulphurous  acid  can  escape.  Previous  to 
DongalFs  invention,  W.  Y.  Turner  had  in  1872  obtained  a 
patent  on  forcing  air  through  closed  sulphur  furnaces. 

Upon  nearly  the  same  principle  is  based  a  leach  ap- 
paratus, which  Dr.  A.  Frank  in  Charlottenburg,  has  de- 
signed and  which  does  not  have  the  drawbacks  of  the 
methods  so  far  described.  In  a  lecture,  which  Dr.  Frank 


THE    MANUFACTURE    OF    CELLULOSE.  fi9 

delivered  at  the  convention  of  the  cellulose  manufacturers 
at  Berlin  in  1887,  the  advantages  of  his  plant  were  pre- 
sented and  about  the  disadvantages  of  the  principal  former 
methods  for  leach-making  the  following  was  said:  "Con- 
cerning the  tower  it  must  be  admitted  that  in  principle, 
they  represent  the  simplest  plant,  in  practice,  however, 
first,  the  depending  of  the  draft,  and  with  it,  of  the  whole 
plant,  on  the  outside  weather  conditions  cause  much 
trouble,  and  in  many  instances  this  has  necessitated  the 
providing  of  ventilating  arrangements  worked  by  ma- 
chinery. It  is  not  less  a  drawback,  that  but  few  limestones 
are  perfectly  suitable  for  the  filling  of  the  towers,  as  too 
hard  a  stone  dissolves  too  difficultly  in  the  weak  acid,  while 
soft  or  impure  stones  sink  together  and  hinder  the  free  pas- 
sage of  the  gas.  Another  important  shortcoming  in  con- 
nection with  the  working  of  towers  is  the  continuous  oxy- 
dation  of  a  not  insignificant  quantity  of  the  sulphurous  acid 
into  sulphuric  acid,  not  only  lost  to  the  process,  but  also 
coating  the  limestones  with  almost  insoluble  sulphate  of 
lime  (gyps),  which  prevents  the  further  action  of  the  sul- 
phurous acid.  In  consequence  of  all  these  circumstances 
these  solutions  corne  out  unevenly  and  of  ten  weak,  especially 
in  summer,  and  as  corrections  cannot  well  be  made  while 
the  work  is  going  on,  the  trouble  of  clearing  the  tower  is  in 
such  cases  unavoidable.  In  the  second  method,  based  up- 
on limestone  (battery  with  compressor)  the  difficulties 
caused  by  the  regulation  of  the  draft  in  the  tower,  are  sure- 
ly dispensed  with,  but  the  other  mentioned  troubles  es- 
pecially the  coating  with  gyps  and  the  clogging  with  mud, 
are  still  retained  and  to  this  is  added  the  expense  of  setting 
up  and  maintaining  the  compressor  pump  needed  to  force 
through  the  sulphuric  acid  gas.  Another  shortcoming, 
common  to  both  apparatuses  must  be  considered,  that  in 
consequence  of  their  very  arrangement  for  continuous 
work  they  always  contain  an  excess  of  limestone,  and 
therefore,  as  long  as  they  are  in  good  order,  i.  e.,  as  long  as 
the  lime  charge  is  not  extremely  coated  with  sulphate,  they 
yield  leaches  very  rich  in  monosulphite  of  lime,  but  poor  in 
free,  active  sulphurous  acid,  which  denotes  itself  by  high 
specific  gravity  with  proportionally  low  per  centage 
in  sulphurous  acid.  The  effort  to  remedy  this 
by  charging  the  towers  but  partially  with  limestone,  and 
partially  with  chemically  inactive  porous  substances,  which 


70  THE    MANUFACTURE    OF    CELLULOSE. 

shall  effect  a  distribution  of  the  leach  and  facilitate  absorp- 
tion of  the  sulphurous  acid,  has  certamtly  been  not  alto- 
gether without  success,  but  has  made  the  plant  very  com- 
plicated and  rather  increased  the  other  drawbacks  men- 
tioned (loss  of  sulphurous  acid  by  oxydation,  etc.). 

When  in  place  of  the  solid  carbonate  of  lime  (limestone) 
the  burned  or  quicklime  is  slacked  and  used  in  the  con- 
dition of  milk  of  lime,  a  great  many  of  the  difficulties  men- 
tioned are  done  away  with.  The  absorption  of  the  sul- 
phurous acid  by  caustic  lime  is  affected  much  more  ener- 
getically and  completely  then  by  carbonate  of  lime,  there- 
fore the  chances  for  oxydation  are  lesened,  and  secondly, 
the  apparatuses  can  be  smaller  and  are  more  economically 
attended  to.  Besides,  when  using  caustic  lime  the  work- 
ing is  not  continuous,  as  when  limestone  is  employed,  one 
has  it  in  hand  to  fix  and  regulate  as  desired  the  amount  of 
lime  in  the  leaches.  As  already  mentioned,  two  methods 
of  circulating  the  gas  through  the  milk  of  lime  may  be  em- 
ployed, i.  e.,  drawing  and  forcing.  Of  these  two  methods 
what  appeared  to  be  the  most  simple  has  been  chosen,  by 
placing  behind  the  last  absorption  tank  an  injector  pro- 
ducing a  vacuum,  which  by  its  sucking  action  suffices  to 
keep  the  sulphur  burning  and  to  draw  the  gases  formed 
after  they  have  passed  a  cooler  and  washer,  through  the 
milk  of  lime.  A  closer  examination  of  this  method  soon 
proved  some  considerable  deficiencies,  amon?  them  the  al- 
most enormous  consumption  of  steam  by  the  injectors  used; 
according  to  low  estimates,  with  an  apparatus  producing 
25-30  cubic  meters  of  leach  per  day,  the  consumption  of 
steam  is  equal  to  that  of  a  30  horse  power  engine;  a  second, 
still  more  essential  failing  in  drawing  the  gases  is,  that  the 
saturation  of  the  leach  with  sulphurous  acid  is  thereby 
possible  in  but  a  limited  measure.  Because  low  pressure 
will  exist  in  this  apparatus,  the  liquid  contained  therein 
takes  up  less  sulphuric  acid  than  when  saturated  with  the 
gas  under  full  atmospheric  presure,  just  as  in  a  glass  of 
seltzer  water  the  carbonic  and  gas  would  escape  in  large 
bubbles  when  brought  into  a  room  under  diminished  pres- 
sure. Especially  during  the  hot  summer  months  the  leach- 
es made  by  this  process  therefore  come  out  very  weak.  The 
full  benefit  of  the  advantages  offered  by  working  with 
slacked  lime  can,  however,  be  gained,  when  instead  of  draw- 
ing the  gases,  they  are  forced  through  the  liquid.  Dr. 


THE    MANUFACTURE    OP    CELLULOSE.  71 

Frank  claims  as  advantages  of  his  apparatus  the  following: 
First,  the  apparatus  makes  possible,  independent  of  out- 
side weather  conditions,  the  steady  and  uniform  prepara- 
tion of  the  leaches,  of  which  inside  of  certain  limits  the 
strength  in  lime  as  well  as  in  sulphurous  acid  can  be  per- 
fectly kept  under  control.  The  strength  can  be  raised  up 
to  10 °B.  Second,  the  plant  can  any  time  be  stopped  and 
started  again.  Third,  the  mechanical  power,  necessary  in 
the  plant  is  small,  only  five  to  six  horse  power,  and  for  an 
output  of  30  cubic  meters  in  twenty-four  hours,  but  one 
man  is  required  per  shift.  Fourth,  the  absorption  of  the 
sulphurous  acid  is  complete  and  bad  odors  caused  by  es- 
caping gas  are  entirely  avoided,  so  that  the  plant,  requiring 
but  little  space,  can  be  put  up  in  any  locality  and  a  special 
building  is  not  required.  A  room  of  8x12  is  sufficiently 
large.  Fifth,  in  consequence  of  the  complete  absorption 
and  the  safe  control  of  the  combination  of  the  sulphur  in 
the  furnace  a  better  use  of  the  sulphur  material  is  made, 
so  that  by  this,  as  well  as  by  the  rational  preparation  and 
composition  of  the  leaches,  considerable  saving  in  raw 
materials  (sulphur  and  lime)  is  gained.  Formation  of  gyps 
and  mud  settling  does  not  occur  in  the  apparatus. 
6.  The  apparatus,  of  simple  and  solid  construction,  is  in 
all  its  parts  easily  overseen  and  easy  to  get  at,  and  is  with- 
out easily  destructable  or  sensitive  parts.  7.  The  ap- 
paratus, though  in  the  first  place  constructed  for  the  use 
of  sulphur,  can  nevertheless  be  used  in  connection  with 
pyrite  furnaces.  8.  The  apparatus  also  makes  it  possible 
to  retain  and  use  over  again  the  sulphurous  acid  blown  off 
from  the  digester,  without  much  additional  cost  and  with- 
out violating  existing  patent  rights.  9.  The  cool  water 
required  by  a  large  sized  apparatus  amounts  to  200-300 
liters  per  minute.  10.  Delay  of  work  by  sublimation  or 
clogging  of  the  pipes  is  altogether  excluded  and  all  in- 
jury to  workmen  as  well  as  to  the  neighborhood  by  es- 
caping sulphurous  acid  is  absolutely  avoided. 

In  regard  to  point  7  it  may  be  mentioned  that  the  author 
was  informed  that  the  Frank  apparatus  could  not  be  ad- 
vantageously used  in  connection  with  pyrite  furnaces,  be- 
cause the  gases  coming  from  pyrite  furnaces  are  poorer  in 
sulphurous  acid  and  richer  in  oxygen  and  because  in  a 
solution  of  bi-sulphite,  oxidation  is  going  on  quicker,  and 
considerable  deposition  of  sulphate  of  lime  takes  place  in 


72 


THE    MANUFACTURE    OP    CELLULOSE. 


the  lime  milk  tanks.  On  account  of  direct  assistance  from 
Hen*  D.  Frank,  the  author  is  able  to  give  the  following  de- 
scription of  his  apparatus: 

The  plan  of  Frank's  leading  apparatus  can  be  seen  in 
figs. 38  and  39.  By  means  of  the  air  pump  B,  which  mav 
be  worked  by  water  or  steam  power  and  which  is  provided 
with  the  air  chamber  C,  the  air  necessary  for  the  combus- 
tion of  the  sulphur,  is  forced  into  the  well  closed  sulphur 
furnace  A,  in  such  exactly  measured  quantities  that  gases 
of  high  grading,  rich  in  sulphurous  acid,  are  obtained.  Be- 
cause the  furnace  itself  as  well  as  the  cooler  D  and  the 
dust  chamber  E,  arranged  in  the  back,  are  kept  cool  and  as 
the  supply  and  distribution  of  the  air  in  the  furnace 


Fig.  38. 

A  is  done  in  a  peculiar  manner,  which  also  make 
entirely  secure  the  burning  of  any  evaporated  sulphur, 
sublimation  of  the  sulphur  and  clogging  of  the  cool- 
ing pipes  can  never  occur.  From  the  dust  chamber 
E  the  gases  then  go  to  the  cooling  coil  F,  surrounded  by 
water,  which  in  order  to  make  the  consumption  of  water 
as  small  as  possible  are  constructed  according  to  the  coun- 
ter current  principle.  From  there  the  gases  go  to  the 
small  washer  1,  in  which  the  small  residue  of  sulphurous 
acid  gas  is  retained.  The  cooled  and  purified  gases  then  en- 
ter the  absorption  battery,  composed  of  three  vessels.  These 
three  vessels  are  placed  one  above  the  other  in  such  man- 
ner that  the  gases  first  pass  througih  the  solution  in  tank 
2,  the  one  most  saturated  with  sulphurous  acid  and  are 
by  the  adding  of  water  diluted  to  the  required  strength. 
Then  they  enter  tank  3,  filled  with  a  stronger  milk  of  lime 
and  lastly  the  uppermost  tank  4,  charged  with  fresh  milk  of 


THE    MANUFACTURE    OP    CELLULOSE. 


73 


lime.  Basins  2  and  3  are  tightly  covered  so  that  the  gases 
can  be  forced  through.  Basin  4  may  be  covered,  but  as  the 
last  traces  of  sulphurous  acid  gas  entering  in  there  are 
rapidly  and  completely  absorbed,  it  is  generally  left  open, 
because  trouble  from  escaping  gas  does  not  O'ccur. 

When  the  leach  has  become  thoroughly  saturated  with 
the  sulphurous  acid,  which  can  be  determined  in  three 
minutes  by  a  sample  taken  any  time  during  work,  the 
sulphur  burning  in  furnace  A  is  put  out  by  simply  stop- 
ping the  air  from  the  compressor  and  thus  ceasing  at  once 


all  evolution  of  sulphurous  acid,  of  which  also  nothing  can 
go  back  into  the  room,  because  the  furnace  is  closed.  The 
finished  leach  in  tank  2  is  then  run  out  and  from  tank  3 
the  concentrated  half  finished  milk  of  lime  is  let  over 
through  a  pdpie  in  the  bottom,  closed  by  a  valve,  and  water 
is  added.  Into  the  emptied,  tank  3  the  leach  from  tank  is 
then  run  over  and  the  latter  is  filled  again  with  fresih 
strong  milk  of  lime,  which  has  been  previously  prepared 
in  a  box  arranged  above  tank  4  from  a  measured  quantity 
of  burned  lime.  The  whole  operation  of  emptying  and 
filling  over  does  not  require  over  30  minutes.  When  this 
is  done,  the  furnace,  meanwhile  thoroughly  cooled  off,  is 


74  THE    MANUFACTURE    OF    CELLULOSE. 

opened  and  again  charged  with  a  weigfhed  quantity  of  sul- 
phur, and  after  this  has  been  ignited,  the  operation 
is  started  again  by  reversing  the  air  pump.  According  to 
the  size  of  the  different  parts  of  the  apparatus,  wlhich  can 
be  exactly  calculated  in  advance,  10  to  20  cubic  meters  of 
leach  can  be  finished  in  one  operation  and  as  the  time  re- 
quired by  one  operation,  including  all  side  work,  as  feed- 
ing of  the  furnace  and  filling  over  of  the  tank?,,  doe®  not 
exceed  seven  hours,  the  capacity  of  a  small  sized  apparatus 
is  about  30  to  35  cubic  meters  per  double  shift  and  of  a 
large  one  about  54  to  60  c.  m.,  whereby  the  labor  of  the 
attention,  besides  controlling  the  burning  of  the  sulphur  in 
the  furnace,  is  limited  to  the  opening  and  closing  of  some 
valves  and1  slaking  of .  lime,  which  occurs  about  three 
times  every  double  shift. 

To  arrange  the  apparatus  for  continuous  working,  i.  e., 
with  continuous  discharge  of  leach  and  charging  with 
fresh-  milk  of  lime,  is  certainly  also  easy,  but  W.  Frank 
gives  decided  preference  to  the  intermittent  method  here 
described,  in  which  the  charge  of  the  large  tank  is  al- 
ways finished  and  discharged  at  once,  because  in  this  way 
the  exact  control  of  the  process,  especially  of  the  proper 
composition  of  the  leach,  is  much  safer.  The  strength  of 
the  gases  in  the  sulphur  furnace  can  also  be  by  this 
method  exactly  adapted  to  the  existing  requirements  by 
regulating  the  air  pump. 

With  Frank's  apparatus  sulphite  leach  can  be  prepared 
from  lime,  dolomite,  pure  magnesia,  and  also  from  soda, 
in  any  strength  up  to  10°  B  and  perfect,  considering  the 
circumstance,  that  the  leaches  made  with  it  from  lime 
cannot  deposit  mono  sulphate  (gyps.)  in  the  digester. 

W.  Frank's  remarks  about  the  disadvantages  of  the 
towers,  wlhich  are  quite  correct,  cannot,  however,  be  con- 
sidered right  in  regard  to  the  Kellner  process.  Mitscherlich 
has  at  the  same  time  used  his  towers  for  aspirators.  But 
the  aspirating  effect  is  continuously  influenced  and  with 
bad  effect  by  changes  in'  the  specific  gravity  of  the  outside 
air  (change  of  temperature,  etc.)  as  well  as  by  the  con- 
tinuous changing  of  the  exposed  surfaces  of  tlhe  limestones 
and  of  the  water,  drizzling  do>wn.  The  gases  also  must 
enter  the  tower  with  high  temperature,  because  otherwise 
there  would  exist  no  difference  in  weight  between  the  al- 
ready heavy  sulphurous  acid  and  the  outer  air,  or  in  other 


THE    MANUFACTURE    OF    CELLULOSE.  75 

words,  no  draft  would  exist.  These  disturbing  factors  are 
avoided  by  Kellner  in  such  manner  that;  1,  the  sulphurous 
acid  is  much  cooled  down;  2,  thegases  are  pressed  forward 
under  low  pressure  through  the  chambers  or  towers  or 
tanks  filled  with  limestone.  Entire  independence  of  the 
variations  noted  is  thus  gained  and  a  series  of  absorption 
apparatuses,  as  long  as  desirable,  can  be  connected,  so  that 
a  perfect  absorption  of  the  sulphurous  acid  can  be  se- 
cured. By  this  means  it  is  just  as  easy  to  regulate  the 
proportion  of  the  sulphurous  acid  tc  the  lime  or  in  other 
words,  of  the  free  and  combined  sulphurous  acid,  by  filling 
part  of  the  absorption  apparatus  not  with  limestones.,  but 
with  an  indifferent  material,  like  pieces  of  brick,  pebble- 
stones, etc.,  and  consequently  the  bisulphite  solution  ob- 
tained from  the  limestones,  *$  enriched  with  as  much 
sulphurous  acid  as  deemed  desirable. 

The  exhausting  of  the  sulphur,  according  to  the  simple 
method  reported  by  Dr.  Frank  in  the  Papier  Zeitung,  is 
determined  by  measuring  the  produced  leach  and  tit- 
rating for  sulphurous  acid  with  iodine.  As  one  pel- 
cent  sulphurous  acid  corresponds  to  the  10  kilograms 
contained  in  the  cubic  meter,  and  one  part  of  chemically 
pure  sulphur  in  complete  combustion  yields  two  parts  of 
sulphurous  acid,  theoretically  5  kilograms  of  pure  sulphur 
should  yield  10  kilograms  of  sulphurous  acid;  however,  the 
second  quality  sulphur  used  in  most  factories  generally 
contains  but  98  p'er  cent  and  as  on  account  of  moisture 
in  the  air  used  in  combustion,  the  formation  of  small  quan- 
tities of  sulphurous  acid  is  never  entirely  excluded,  and 
when  discharging  and  filling  over  small  losses  of  leach  can- 
not be  avoided,  Dr.  Frank  guarantees  95  per  cent  consum- 
mation of  the  sulphur  charged  to  the  furnace,  so  that  of 
100  kilo  sulphur,  weighed  and  charged  to  the  furnace,  190 
kilo  effective  gaseous  sulphurous  acid  in  the  leaches  are 
obtained.  That  in  careful  working  a  higher  result  may 
be  obtained,  is  shown  by  the  results  from  the  factory  of 
J.  Spiro  &  Son  in  Bohmisch— Krumau,  published  by 
Kymmene  Bruck,  according  to  which  the  exhaustion  of 
sulphur  reaches  96.8-97  per  cent;  consequently  from  100 
kilo  of  sulphur  193.6-194  kilo  of  sulphurous  acid  were  pro- 
duced. 

Regarding  the  composition  of  leaches  produced  with 
Frank's  aparatus  already  mentioned,  Dr.  Frank  has,  on  the 


76  THE    MANUFACTURE    OF    CELLULOSE. 

basis  of  scientific  investigation,  which,  have  been  more  fully 
confirmed  by  results  obtained  by  working  on  a  large  scale, 
secured  the  taking  of  the  percentage  of  lime  in  the  leach  as 
low  as  possible,  as  the  main  effect  depends  on  tihe  free  ac- 
tive sulphurous  acid  only,  while  a  high  percentage  of  lime 
besides  other  uncertainties,  requires  unnecessary  con- 
sumption of  sulphurous  acid,  i.  e.,  of  sulphur  material. 
In  proof  of  this,  Dr.  Frank  quotes  the  following  example: 
A  factory  leach  A  of  7°B  contained,  total  sulphurous  acid, 
4.35;  of  this,  free  acid,  2.35;  of  combined  acid,  2.00;  and 
lime  corresponding  to  the  latter,  1.75. 

A  leach  of  nearly  5°B  prepared  in  Dr.  Frank's  ap- 
paratus, with  which  the  boiling  was  effected  in  exa,ctly  the 
same  time,  but  without  formation  of  sulphate  (gyps.)  con- 
tained: Total  sulphurous  acid,  3.254;  of  this  free  acid, 
2.382;  of  this  combined  acid,  0.874;  aind  lime  correspond- 
ing to  the  latter,  0.764. 

It  can  be  noticed  that  the  leach  B,  regardless  of  its  low 
specific  gravity  and  low  percentage  of  total  sulphurous 
acid,  is  richer  in  free  active  sulphurous  acid  than  the 
heavy  leadh  A,  also,  while  the  preparing  of  the  latter  in 
Frank's  apparatus  requires  at  95  per  cent  expansion  about 
23  kilos  of  sulphur  per  cubic  meter  leach,  for  the  same 
quantity  of  leach  B  but  17  kilo  of  sulphur  are  necessary, 
so  that  besides  the  considerably  higher  effectiveness  of  all 
apparatuses,  with  the  rationally  composed  weaker  leach  a 
direct  saving  of  6  kilos  of  sulphur  per  cubic  meter  leach 
is  gained. 

In  the  further  working  of  the  material  produced  with 
both  leaches  at  the  factory  mentioned  it  has  been  settled 
that  the  cellulose  digested  with  the  7°  leach  yielded  1.85 
per  cent  ashes,  while  tihie  one  boiled  with  the  weaker  leach 
gave  but  0.36  per  cent. 

For  the  expert  in  the  matter  it  need  hardly  be  mentioned 
that  there  can  be  no  general  directions  in  regard  to  the 
composition  of  the  leaches,  suitable  for  every  kind  of 
wood,  as  well  as  for  all  methods  of  boiling,  but  that  such 
must  be  conformed  to  material  and  process.  Where  the 
steam  does  not  enter  directly  into  the  boiler  the  leaches 
do  not  get  diluted  and  a  weaker  solution  can  be  worked, 
but  when  the  steam  enters  directly,  especially  when  it  is 
not  sufficiently  dry,  weak  and  dilute  leaches  are  caused. 
So  for  instance  at  the  factory  in  Kruman  with*  digesters 


THE    MANUFACTURE    OF    CELLULOSE.  77 

according  to  the  Mitscherlich  system  a  leach  of,  total  sul- 
phurous acid,  3.035;  of  which  free  acid,  2.023;  of  which 
combined  acid,  1.012,  and  lime  corresponding  to  the  lat- 
ter, 0.827,  for  which  but  16  kilos  of  sulphur  per  cubic 
meter  were  necesary,  has  proved  entirely  sufficient. 

Against  the  7°  leach,  mentioned  above,  a  saving  of  60 
marks  per  day  would  result  at  a  daily  consumption  of 
about  80  cubic  meter  leach. 

Quite  a  large  number  of  Frank's  apparatuses  have  been 
in  use  some  years,  in  connection  with  different  systems  of 
digesting. 

According  Lo  information  from  the  machine  works  of 
Grolzern  the  price  for  one  leaching  aparatus  of  50  cubic 
meter  daily  capacity,  completely  mounted,  put  in  working 
order  and  delivered  with  reference  to  the  exhausting  of  the 
sulphur,  as  guaranteed,  is  about  24,000  marks,  inclusive  of 
license  and  mounting.  The  daily  production  of  50  cubic 
meters  of  leach  of  3.3  per  cent  sulphurous  acid  and  1  per 
cent  lime  costs: 

For  870  kilos  sulphur  at  11.00  marks  per  100  kilos,     95.70 
For  550  kilos  burned  lime  (including  loss  in  slak- 
ing) at  1.50  marks  per  100  kilos 8.25 

Wages  for  2  shifts  at  2.50  marks  5.00 

Power  of  5  to  6  horse  (if  not  furnished  by  water 
motor)  at  2.5  kilos  ooet  per  hour  and  horse-power 

calculated  per  ICO  kiloo  ait  1.50  marks 6.00 

Lifting  of  200  to  300  liter  cool  water  per  minute, 

light,  lubricants,  etc .'....       5.00 

5  per  cent,  interest,  10   per   cent,   amortization   of 

24,000.00  marks  per  day 12.00 


M132.00 
or  264  marks  per  cubic  meter. 

Besides  the  low  cost  of  production,  the  special  ad- 
vantage is  gained  against  the  use  of  pyrite,  that  the 
working  of  the  aparatus  can  be  started  and  stopped  at  any 
moment,  and  the  accummulatioii  of  the  residue  pyrite,  so 
annoying  in  many  factories,  is  done  away  with. 

The  method  of  Dr.  Frank  has  in  recent  years  on  account 
of  its  advantages  come  more  and  more  into  use  because  the 
making  of  leaches  with  it  is  in  fact  very  clean,  handy  and 
uniform,  and  entirely  independent  of  the  season.  As  figs. 
38  and  39  will  show  the  arrangement  of  the  Frank  plant, 


78 


THE    MANUFACTURE    OP    CELLULOSE. 


but  do  not  give  a  distinct  picture  of  the  form  of  the 
sulphur  furnace  proper,  two  cuts,  fig.  40  and  41,  have 
been  added.  It  can  be  seen  that  the  sulphur  furnace  0  has 
the  shape  of  a  flat  tube,  withi  both  ends  made  of  cast  iron, 
the  level  bottom  almost  entirely  taken  up  by  the  low  sul- 
phur pan  S.  The  sulphur  to  be  burned,  previously 
weighted,  is  put  in  the  pan  through  the  door  T,  there 
spread,  and  lighted  by  means  of  a  red  hot  iron  bar.  The 


FIG.    40. 


FIG.    41. 

right  state  of  combustion  can  at  any  time  be  closely  con- 
trolled through  the  hole  1  in  the  door,  covered  with  a 
strong  plate  of  glass.  When  the  flame  is  burning  deep 
blue,  all  is  in  good  order,  but  if  by  evaporating  sulphur 
colored  yellowish-brown,  more  air  must  be  admitted.  The 
supply  of  air  and  the  regulating  is  done  through  the  two 
pipes  rl  and  r2,  whicih  may  be  totally  or  partially  closed 
by  valves.  In  order  that  the  air  may  come  in  close  contact 
with  bairning  sulphur  at  the  rear  end  of  the  furnace  a  par- 
tition W  reaches  from  the  ceiling  down  near  to  the  pan, 
so  that  the  air  together  with  the  evolved  gas  must  strike 
clos'e  over  the  pan  before  it  leaves  tihe  furnace  at  C  and  is 
carried-  away,  as  already  described. 

In  comparison  with  the  pyrite  furnaces,  which  produces 


THE    MANUFACTURE    OP    CELLULOSE.  7» 

gases  of  only  about  8  per  cent>  the  sulphur  furnaces  works 
considerably  better,  because,  as  already  mentioned,  the  air 
supply  a  n  be  exactly  measured  and  gases  of  up  to  15  per 
cent  can  be  produced. 

The  leach,  plant  of  Frank's  differs  from  a  pyrite  furnace 
plant  not  only  in  the  absence  of  the  pungent  smelling 
sulphurous  acid,  but  also  in  avoiding  all  radiation  of  heat. 
This  is  attained  by  placing  the  entire  retort  inside  of  a 
large  box,  K,  of  sheet  iron,  near  the  bottom  of  which  cold 
water  is  continuously  running  in  at  e,  surrounding  the  re- 
tort and  cooling  it  and  running  off  again  as  warm  water 
at  the  top  at  a.  In  this  manner  it  is  not  only  much  more 
pleasant  to  stay  in  a  factory  with  one  01  more  Frank  ap- 
paratuses, but  at  the  same  time  all  annoyance  to  the  neigh- 
borhood, as  well  as  therefrom  resulting  damage  suits  are 
done  away  with. 

In  most  of  the  sulphur  furnaces  of  this  system  in  use 
about  1,500  kilos  of  sulphur  can  be  burned  in  24  hours. 
This  quantity  is  sufficient  for  most  factories,  but  it  is  ad- 
visable to  have  a  complete  apparatus  in  reserve  so  that 
in  case  of  any  irregularities  it  does  not  become  necessary 
to  stop  the  operating  of  the  whole  plant.  At  times,  when 
the  apparatus  is  not  in  use,  it  can  advantageously  be  other- 
wise employed.  Thus  the  tanks  may  be  fitted  with  milk  of 
lime,  the  excess  of  sulphurous  acid  in  the  digester  blown 
into  them,  and  so  not  a  small  quantity  of  leach  of  various 
strengths  is  easily  obtained. 

Some  variation  from  the  already  described  methods  and 
a  similiarity  with  the  Douglas  process  is  marked  in  the 
system  of  leach  making  by  the  Englishman,  Edward 
Partington,  whose  process  is  explained  as  follows:  This  in- 
vention relates  to  the  manufacture  of  sulphurous  acid  and 
its  combinations  by  a  continuous  process,  the  essential  of 
which  is  tihat  the  water  or  the  alkaline  solution  enters  by 
gravity  from  one  tank  into  another,  while  gaseous  sul- 
phurous acid  at  the  same  time  is  circulating  in  an  opposite 
direction  successively  through  the  water  or  alkaline  solu- 
tion in  each  receiver,  while  the  water  or  alkaline  solution 
is  kept  in  constant  motion,  by  a  rotating  stirring  arrange- 
ment. In  the  accompanying  fig.  42,  three  receivers  A,  Al, 
and  A2  are  shown,  wihile  at  the  cover  as  well  as  at  the 
bottom  are  in  connection  with  each  other  for  a  purpose 
later  on  explained.  Each  of  the  receivers,  which  are  made 


80  THE    MANUFACTURE    OF    CELLULOSE. 

of  wood  or  any  other  material  suitable  for  the  manufac- 
ture of  sulphurous  acid,  or  sulphites  and  bisulphites  of 
the  alkalines  and  alkaline  earths,  consist  of  a  cover  a,  the 
bottom  al  and  the  sides  a2,  the  latter  being  cylindrical. 
The  side  walls  of  every  cylinder  carry  the  traverses  b  (fig. 
42),-  to  which  are  fastened  the  stands  bl  bearing  the  shaft 
b2,  with  fixed  and  loose  pulley,  to  drive  by  belt.  At  one 
end  of  the  shaft  b2  is  the  bevelled  gear  b4,  driving  the 
wheel  b5  on  the  shaft  b6,  going  through  the  stuffing  box 
b7,  fixed  to  the  cover  a,  into  the  tank.  The  shaft  b6  is 
held  at  its  upper  end  by  a  frame  and  reaches  almost  to  the 
bottom  of  tank  Al.  It  is  provided  with  the  bars  d,  con- 
nected by  the  cross  bars  dl,  forming  together  with  the 
shaft  a  stirring  arrangement  by  which  the  liquid  iu  space 
B  of  the  tank  can  be  stirred  about. 

The  liquid  for  making  the  sulphurous  acid  can  be  either 
water,  or  any  solution  containing  a  substance  which  can 
with  sulphurous  acid  form  sulphites  or  bisulphites.  For 
the  present  case  calcium  hydrate  is  supposed  which  enters 
the  tank  A  near  its  cover  through  the  pipe  e.  The  tank 
Al  connected  by  the  pipes  el,  e2;  the  pipe  el  leads  from  the 
bottom  in  A  below  the  cover  of  Al,  while  pipe  e2  goes 
from  the  cover  of  A  to  the  bottom  of  the  tank  Al — Al  is 
connected  with  A 2  in  similar  manner  by  the  pipes  e3  and 
e4,  of  which  e3  leads  from  the  bottom  of  tank  Al  below 
tihe  cover  of  A2  and  e4  reversed.  The  tank  A2  is  in  the 
same  manner  provided  with  the  pipes  e6  and  e7,  which 
are  shown  broken  off  in  the  sketch,  to  connect  another 
tank  in  the  same  manner.  The  pipes  el  and  e3  are  pro- 
vided with  valves,  by  which  the  connection  between  the 
tanks  is  broken.  When  beginning  work,  the  valves  are 
closed,  whereupon  the  liquid  is  run  into  tank  A  through 
pipe  e.  In  practice  it  is  preferable  to  have  the  liquid  con- 
stantly run  in  during  the  operation,  so  that  it  runs  from 
A  through  the  pipe  e2  into  Al,  from  Al  through  e4  into  A2 
and  from  A2  through  e7  out.  By  the  gravity  of  the  liquid 
a  constant  flow  through  the  tank  is  thus  maintained  and 
a  current  of  sulphurous  acid  is  drawn  in  the  opposite  direc- 
tion through  the  liquid  by  means  of  an  exhauster,  not  vis- 
ible in  the  sketch,  connected  to  tank  A  by  pipe  f3.  The 
gas  is  first  admitted  through  the  pipe  f  to  the  inner  or 
space  B  of  the  tank  A2,  where  it  enters  into  two  places  at 
the  bottom  and  goes  from  space  B  through  pipe  fl  into  space 


THE    MANUFACTURE    OP    CELLULOSE. 


81 


B  of  tank  A^  from  there  through  pipe  12  into  space  B  of 
tank  A  and  is  drawn  out  through  pipe  f3.  During  the  pro- 
cess gases  and  liquid  are  well  mixed  by  the  stirring  ar- 
rangement,, which  can  be  driven  by  the  arrangement  de- 


scribed or  in  any  other  suitable  manner.  The  liquid 
transformed  into  sulphurous  acid  or  sulphite  o>r  bi-sul- 
phite  flows  from  tank  A 2  through  the  outlet  pipe  e7  and 
is  then  ready  for  use.  The  finished  leach  runs  into  four 


82  THE    MANUFACTURE    OF    CELLULOSE. 

air  tight  storage  tanks,  10x10x8,  and  is  from  there  pumped 
to  the  digesters. 

In  Partingtori's  factory  the  sulphurous  acid  is  produced 
in  a  sulphur  furnace  of  2x8,  by  burning  of  pure  regener- 
ated sulphur  of  99  per  cent,  and  of  pyrite  (with  48  per 
oent.  sulphur)  and  it  first  circulates  through  a  system  of 
pipes,  cooled  with  waiter,  before  it  is  permitted  to  enter 
near  the  bottom  of  the  lowest  tank. 

After  the  preparing  of  leaches.,  as  performed  according 
to  the  methods,  mostly  employed  in  Germany  and  Eng- 
land, has  been  fully  described,  some  other  methods,  as 
given  by  Professor  Hoyer  in  his  book,  shall  for  the  sake 
of  completeness  be  shortly  treated  in  this  chapiter. 

Eckman  uses  as  leach  a  solution  of  sulphite  of  magne- 
sia, which  contains  two  equivalents  of  sulpihiurous  acid 
for  one  equivalent  of  magnesia  and  in  such  concentration 
that  almost  1.4  per  cent  magnesia  and  4.4  per  cent  sul- 
phurous acid  are  present  in  it.  To  prepare  the  sulphite, 
Grecian  or  German  magnesite  is  calcined  in  lime  kilns, 
then  in  tower's  of  lead  (with  inside  wood  lining  to  protect 
the  lead)  exposed  to  sulphurous  acid,  produced  from  sul- 
phur and  to  water  drizzling  down  and  finally  discharged 
as  sulphite  solution1. 

In  the  process  of  Fraiike  in  (Sweden)  a  solution  of  acid 
sulphite  of  lime  is  employed,  made  by  leading  hot  sul- 
phurous acid,  produced  by  roasting  pyrite  in  a  to-wer 
13  meters  high,  divided  into  several  vertical  chambers, 
which  are  filled  with  limestones  and  which  can  be  charged 
and  attended  to  independently  of  each  other,  and  to  which 
water  is  admitted  from  above  in  quantities  just  sufficient, 
so  as  tio  secure1  a  warm  solution,  at  once  ready  for  use.  The 
solution  is  run  into  receivers  of  cement,  lined  with  lead 
and  from  there  it  is  pumped  to  the  digester. 

In  the  method  of  Graham  in  London,  at  first  only  the 
solution  of  the  monosulphites  of  any  base  (potash,  soda, 
magnesia)  is  charged  into  the  digester  and  after  it  has 
been  freed  from  air  and  carbonic  acid,  the  effective  com- 
bination is  produced  by  pumping  in  sulphurous  acid  gas 
or  solution.  In  this  method,  which  is  effected  in  a  ver- 
tical digester  with  steam  jacket,  the  escape  of  acid  is  pre- 
vented in  the  first  place,  but  the  liquid  is  steadily  main- 
tained in  equal  strength  by  filling  up  from  the  bottom, 
when  necessary. 


THE    MANUFACTURE    OF    CELLULOSE.  83 

The  method  of  Picket  in  Lausanne,  (D.  K.  P.  25331)  is 
based  on  the  theory  that  in  consequence  of  the  high  tem- 
perature now  generally  used,  the  gums  and  resins  in  the 
wood  are  changed  into  tar  and  thus  render  so  difficult  the 
bleaching  of  tihe  product  that  it  is.  practical  to  employ  a 
solution,  of  sulphurous  acid,  which  would  disolve  the  in- 
crusting  substances  at  a  lower  temperature.  For  this 
purpose  Picket  recommends  an  aqueous  solution  of  sul- 
phurous acid.  But  as  100-500  grams  of  sulphurous  acid 
have  to  be  dissolved  in  1  liter  of  water  to  obtain  a  pres- 
sure of  from  5-7  atmospheres  at  a  temperature  of  80- 
90°  0  in  the  digester,  liquid  sulphurous  acid  anhydride  is 
charged  into  the  digester  under  pressure  under  the  above 
mentioned  conditions.  The  acid  mixes  with  the  water  and 
yields  the  desired  solution,  which  in  the  digester  by  steam 
evils  is  raised  to  the  the  temperature  of  not  over  85  °C,  be 
cause  at  90 °C  carbonization  would  begin.  To  make  the 
liquid  thoroughly  penetrating,  it  is  recommended  to  pro- 
duce a  vacuum  before  it  is  charged  to  the  digester,  to  open 
the  pores  of  the  wood. 

The-  agueous  solution  prepared  according  to  this  method 
(without  alkali)  contains  about  1  1-2  to  2  per  cent  of  sul- 
phurous acid.  When  the  necessary  quantity  of  this  acid 
together  with  the  wood  is  charged  into  the  digester,  in 
another  boiler  a  liquid  of  the  same  kind  is  heated  to  about 
100°  and  the  sulphurous  acid  thus  set  free  is  driven  over 
to  the  digester  until  the  leach  in  there  contains  ,2  per 
cent  acid.  After  the  operation  is  finished,  the  acid  is 
driven  off  in  the  same  manner  and  used  for  the  preparation 
of  new  leaches.  The  highest  temperature  employed  is 
105  °C.  The  essential  difference  of  this  method  in  com- 
parison with  other  sulphite  processes  is  therefore,  that  no 
lime  is  contained  in  the  solution,  while  a  small  per  centage 
is  really  necessary  in  order  to  neutralize  the  sulphuric  acid, 
which  forms.  The  resulting  product  is  less  white  than 
with  other  methods. 

According  to>  Flodgnist  in  Gothenburg,  in  preparing  the 
digesting  liquid,  the  sulphurous  a,cid  is  partially  led  over 
limestone,  partially  over  bones,  the  fat  of  which  has  been 
extracted,  which  are  piled  up  in  towers  or  chambers,  to 
form  a  mixture  of  sulphite  and  phosphate  of  lime  and  be- 
sides to  produce  glue  material  for  the  manufacture  of  glue, 
wherefore  always  several  chambers  (as  already  mentioned, 


84  THE    MANUFACTURE    OP    CELLULOSE. 

as  many  as  10)  are  in  use,  so  that  one  after  the  other  can 
be  disconnected  for  discharging  and  refilling,  as  necessary. 

The  method  of  Archfoold  in  Oswego,  is  based  on  the 
principle  to  produce  sulphite  of  lime  directly  upon  the 
fibre,  in  order  to  make  it  thus  a.ct  so  much  more  power- 
fully. To  this  purpose  the  raw  materi*^  i.  e.,  the  dressed 
wood,  is  first  saturated  in  the  digestel  /ith  milk  of  lime, 
which  consists  of  from  1  to  6  parts  of  lime  in  100  parts  of 
water,  and  for  hard  wood,  also  1  part  of  nitrate  of  lime. 
Then  sulphurous  acid  (either  in  gaseous  or  in  liquid  form) 
is  charged  to  the  digester  and  after  about  five  minutes  it  is 
exposed  to  a  pressure  of  from  4  to  5  atmospheres  and  some- 
times,, according  to  the  kind  of  wood,  for  one  to  two  hours 
and  a  half 

At  the  end  of  this  chapter  about  leaches  and  leach- 
making  in  regard  to  sulphite  leaches  it  must  be  mentioned 
again,  that  measuring  the  concentration  with  the  areo- 
meter, in  use  in  most  factories,  does  not  give  a  correct  re- 
sult, and  to  the  advantage  of  the  digesting  operation  it  is 
highly  desirable  that  the  leaches  be  tested  every  time  before 
using,  by  analysis,  for  their  strength  in  active  sulphurous 
acid.  This  is  possible  without  a  complete  laboratory  out- 
fit, by  the  following  method  of  Dr.  E.  Hoehn,  based  on  the 
reaction  of  iodine  on  sulphurous  acid  under  decomposition 
of  water,  forming  hydroiodic  acid  on  the  one  side,  and 
sulphuric  acid  on  the  other.  When  therefore  a  solution  of 
pure  sulphurous  acid  is  extricated  and  to  this  for  instance 
10  cubic-centimeters  one-tenth  normal  iodine  had  to  be 
used,  at  the  end  of  the  reaction  the  liquid  will  contain  a 
certain  quantity  of  hydroiodic  acid,  corresponding  to  10 
cubic-centimeters  one-tenth  normal-iodine,  and  an  equal 
amount  of  sulphuric  acid,  so  that  in  neutralizing  the  acid 
formed  by  an  alkali,  20  cub'c-centimeters  one-tenth  nor- 
mal-soda will  be  necessary.  But  in  place  of  uncombiaed 
free  sulphurous  acid  in  the  solution  to  be  tested,  there  is 
an  acid  sulphite,  for  instance,  of  lime,  the  same  amount  of 
sulphuric  acid  is  formed  in  the  titration,  but  which  will 
be  partially  neutralized  by  the  base  already  existing,  so  that 
in  titrating  back  the  two  acids  formed,  the  double  amount 
of  cubic-centimeters  of  iodine  is  not  necessary,  but  much 
less  suffices. 

SODA  PKOCES'S. 

It  lies  in  the  nature  of  the  soda  process,  because  the  so- 


THE    MANUFACTURE    OP    CELLULOSE.  85 

da  employed  therein,  like  the  alkalis  in  general,  does  not 
attack  iron,  that  the  boilers  used  in  manufacturing  soda- 
cellulose  can  be  more  simple,  than  the  sulphite-digesters, 
which  latter  must  be  fitted  with  all  possible  appliances  for 
protection.  According  to  the  method  of  working,  they 
may  have  small  or  large  dimensions,  may  be  fixed  or  rotat- 
ing, placed  horizontal  or  vertical.  In  most  instances  fixed 
vertical  boilers  are  used,  because  the  process  of  boiling 
mostly  takes  place  with  circulation  of  the  leach  and  a 
more  effective  stirring  up  is  not  absolutely  necessary  on 
account  of  the  very  large  dimensions  and  weights  of  some 
of  these  digesters,  it  would  be  both  difficult  and  expensive 
to  make  them  of  the  rotary  pattern. 

The  manufacture  of  soda-cellulose  is  really  not  a  new 
invention,  but  only  a  modification  of  the  method  used  in 
the  manufacture  of  straw-stuff,  as  the  wood  is  boiled  with 
soda  lye  under  pressure  in  a  similar  manner.  It  is  twenty- 
five  years  since  the  present  Commercien-rath  Herr  Max 
Dresel  in  Dalbke,  Germany,  took  upon  himself  this  task 
of  perfecting  this  process,  and  the  author  may  be  per- 
mitted to  give  here,  according  to  the  personal  notes  by 
Herr  Dresel,  a  brief  description  of  the  details  and  results 
of  the  experiments,  made  1871.  First  of  all,  in  1870,  he 
acquired  from  the  engineer  ,James  A.  Lee,  the  rights  and 
models  for  a  chopping  machine,  which  was  previously 
built  after  a  dye-wood  chopper  by  Houghton  in  Manches- 
ter for  the  Gone  paper  mills  in  England.  This  Mr.  Lee 
had  at  the  time  a  small  machine  factory  adjoining  the 
Cone  mills,  near  Sidney,  England,  and  was  engaged  by 
contract  to  repair  and  superintend  the  mechanical  plant. 
In  this  capacity  he  undertook  a  small  change  in  the  Hough- 
ton  wood-cutter  and  then  had  the  whole  machine  patented. 
The  Cone  mills,  in  1870,  were  working  with  very  primitive 
apparatus,  part  of  which  had  been  designed  by  the  engineer 
Houghton,  part  of  which  was  built  after  that  used  by  Jes- 
sup  &  Moore  ,in  Philadelphia,  for  the  boiling  of  straw  and 
poplar  wood,  producing  very  imperfect  brown  half-cellu- 
lose, which  they  were  not  able  to  bleach  and  which  could 
be  only  employed  for  brown  packing  paper.  On  a  voyage, 
undertaken  in  1870,  to  England,  Herr  Dresel,  while  not 
allowed  to  inspec+  the  Cone  mills,  found  out  that  the 
boilers  used  in  this  factory  for  boiling  straw  and  wood 
were  designed  by  Mr.  Houghton,  who  held  a  patent  on 


86  THE    MANUFACTURE    OP    CELLULOSE. 

them.  These  boilers  were  horizontal  cylinders,  lined  with 
a  large  system  of  pipes  and  the  boilers  themselves  lay  in 
the  open  fire.  This  pipe  system  was  fed  with  water,  thus 
heating  the  contents  of  the  boiler. 

In  France,  by  the  courtesy  of  the  paper  manufacturer, 
Dambricourt,  in  St.  Omer,  he  examined  a  large  straw 
boiler,  which  lay  in  direct  fire,  and  had  a  large  stirring 
arrangement  inside,  in  which  poplar  wood  was  being  boiled 
experimentally.  According  to  the  observations  there  made 
Herr  Dresel  concluded  that,  when  with  a  boiler  with  di- 
rect firing,  without  a  stirring  inside,  as  in  the  Cone  mills, 
poplar  wood  could  be  boiled,  and  when  this  was  also  pos- 
sible, as  in  St.  Omer,  with  direct  heating  in  a  horizontal 
cylindrical  boiler  with  stirrer,  it  would  also  be  possible  to 
boil  wood  in  a  horizontal  cylindrical  boiler  with  direct  fire 
and  without  inside  stirring  arrangement. 

After  wearisome  trials  he  succeeded  in  finding  a  pro- 
cess of  boiling  with  caustic  soda  in  a  small  experimental 
boiler,  which  promised  to  answer  also  on  a  large  scale  for 
the  dissolution  of  fir,  and  especially  of  pine  wood.  He 
then  ordered  a  boiler  forty-five  feet  long  and  four  feet  in 
diameter,  designed  for  ten  atmospheres  practical  pressure. 
After  a  complete  plant  had  been  finished,  the  large  wood 
digester  was  put  to  work  on  October  1,  1871,  and  thus  the 
first  wood  fibre  factory  on  the  continent  was  opened.  To 
procure  a  practical  scaling  arrangement,  which  could  stand 
the  necessary  high  pressure,  caused  especial  difficulties,  but 
it  should  be  considered,  that  in  the  beginning  any  leading 
points  and  examples  for  the  preparing  of  leaches  on  a 
large  scale,  as  well  as  for  the  duration  of  the  process  of 
digesting  and  all  other  occurrences  were  unobtainable,  and 
consequently  the  first  period  of  manufacturing  caused  con- 
siderable expenses.  So  much  greater  was  the  satisfaction 
then,  when  the  results  of  the  operations  were  yielding  a 
product,  capable  of  being  bleached,  which  in  many  in- 
stances could  serve  as  substitute  for  rag  fibre  in  the  manu- 
facture of  paper.  The  ideas  worked  out  and  tried  prac- 
tically in  the  first  Dalbke  factory,  were  taken  up  by  the 
above-mentioned  Mr.  Lee,  and  by  the  engineer,  Eosenham, 
employed  by  the  Brackwede  boiler  works,  and  later  intro- 
duced in  Sweden  under  the  name  of  the  Lee  system. 

Regarding  the  process  of  digesting  itself,  a  soda-leach 
of  ten  degreesB,  a  temperature  of  360  degrees  F.,  and  a 


THE    MANUFACTURE    OF    CELLULOSE. 


87 


pressure  of  from  nine  co  ten  atm  Spheres  proved  most  sat- 
isfactory. The  boiler  contained  01  rather  yielded  850  kilo- 
gramme of  dry  stuff. 

After  the  first  large  digester  had  been  in  working  for 
a  longer  period,  a  number  of  disadvantages  were  experi- 
enced with  it,  which  were  principally  that  with  the  inter- 
mittent use,  the  sudden  change  between  strong  heating 
and  cooling  off  caused  leaks  in  the  seams  of  the  boiler, 
which  could  not  be  wholly  avoided  and,  not  considering 
the  large  expense  for  repairing,  caused  heavy  losses  in 
leach.  There  was  also  a  very  unsatisfactory  use  of  the 


Fig  44. 

fuel  with  this  boiler,  and  the  cost  of  heating  was  thus  out 
of  proportion.  Finally  the  cooling  off  could  be  effected 
but  slowly  and  only  with  loss  of  leach.  For  this  reason, 
Herr  Dresel  has  after  much  experimenting  devised  the 
construction,  which  has  been  patented  to  him  under  No. 
5,891,  in  May,  1878,  which  is  based  on  the  principle  of 
heating  the  digester  without  exposing  it  to  the  fire.  This 
is  done  by  direct  heating,  but  without  vapors  and  without 
dilutionof  the  leach,  by  the  automatic  circulation  of  the 
leach,  which  may  be  brought  to  high  pressure  at  will. 
Later  on  he  improved  this  construction,  and  in  1878  he 


88 


THE    MANUFACTURE    OF    CELLULOSE. 


took  out  a  supplementary  patent,  which  principally  con- 
cerned improvements  in  the  pipe-heating  system.  The 
following  figures  show  the  perfected  construction:  The  up- 
right cylindrical  digester  A,  which  is  funnel-shaped  below, 
has  at  the  lower  side  a  manhole  for  discharging  and  on  top 
a  wide  fillhole  with  cover.  In  the  middle  of  the  lower 
bottom  there  is  a  nipple  which  is  directly  connected  with 
the  heating  apparatus  B,  and  also,  if  desired,  with  other 
boilers.  This  connection  may  be  opened  or  closed,  as  re- 
quired, by  cocks  or  valves. 

The  heater  B,  directly  connected  with  the  boiler,  con- 


i    |Qf ' 


Fig.  45. 

sists  of  a  system  of  pipes  R  lying  parallel  either  side  by  side 
or  one  above  the  other,  at  certain  distances  and  with  a  cer- 
tain inclination,  which  end  in  the  narrow  chambers  K. 

The  liquid  with  which  the  digester  is  filled  enters  the 
lower  chamber  at  one  side,  while  the  heated  liquid  ascends 
from  the  upper  chamber  at  the  other  side,  so  that  the 
liquid  in  entering  the  heating  apparatus  fills  all  pipes  at 
the  same  time. 

The  liquid,  which  is  quickly  heated  on  account  of  the 
large  heating  surface,  rises  from  the  heating  apparatu»into 
the  pipe,  discharging  into  the  boiler  at  its  upper  end  and, 
circulating  through  the  digester,  returns  into  the  lower 


THE    MANUFACTURE    OF    CELLULOSE.  89 

heating  pipe  chamber.  In  this  manner  an  automatic  cir- 
culation of  the  liquid  takes  place,  and  the  contents  of  the 
digester  can  thus  be  heated  by  direct  fire,  without  expos- 
ing the  apparatus  itself  to  the  fire.  By  this  arrangement  a 
more  rapid  heating,  energetic  and  even  circulation  in  the 
digester  is  secured  with  almost  no  formation  of  steam. 
There  is  also  a  more  perfect  impregnation  and  more  rapid 
heating  of  the  contents  of  the  digester,  as  compared  with 
a  heating  apparatus  formed  by  a  horizontal  coil,  as  design- 
ed in  the  main  patent. 

These  cellulose  digesters  have  proved  very  successful, 
and  three  of  them  have  been  at  work  since  1877,  without 
one  of  them  having  to  be  repaired.  Moreover,  these  boil- 
ers yield  a  very  good  product,  are  charged  and  discharged 
with  ease,  and  have  the  great  advantage  of  absolute  safety 
and  comparative  cheapness. 

With  these  patent  digesters  there  is  also  the  advantage 
that  with  them  the  operation  can  be  finished  in  from  two 
and  one-half  to  three  hours,  and  that  the  stuff  can  be 
washed  in  them  without  damage  to  the  digester  and  with- 
out loss  of  material;  further,  on  account  of  the  energetic 
circulation,  a  uniform  and  complete  solution  of  the  in- 
crustations is  effected,  which  is  proved  by  the  fact  that 
the  cellulose  made  in  them  can  be  bleached  white  with 
from  8  to  9  per  cent  chloride  of  lime,  while  the  other  soda- 
cellulose  require  12  and  sometimes  even  20  per  cent  of 
chloride  of  lime.  The  boilers  are  used  for  soda,  as  well  as 
for  sulphite-leaches,  which  in  evaporating  furnaces  con- 
structed by  Herr  Dresel  are  evaporated  and  then  calcined 
in  the  so-called  calcining  furnace. 

In  an  American  factory  the  digesters  have  1.5  metres 
diameter  and  5  metres  height.  Inside  there  is  a  perforated 
false  bottom  and  cover,  which  arrangement  is  provided  in 
most  boilers  of  this  kind  so  that  the  wood  cannot  stop  up 
the  tubes,  but  is  retained  in  the  middle  large  space.  The 
soda-leach  has  a  strength  of  12  degrees  Beaumi  and  by  direct 
fire  it  is  gradually  raised  to  the  boiling  point  and  the  pro- 
cess is  finished  at  a  pressure  of  from  six  to  eight  atmos- 
pheres (160  to  172  degrees  C.)  in  about  six  hours.  Dahl, 
in  whose  process  for  100  kilos  of  medium  dry  wood  about 
26  kilos  of  the  salts  are  necessary,  as  mentioned  in  the 
chapter  of  leach-making,  corresponding  to  a  leach  of  from 


90  THE    MANUFACTURE    OF    CELLULOSE. 

six  to  fourteen  degrees  Beaumi,  also  boils  in  iron  digesters 
with  a  pressure  of  from  5  to  10  atmospheres,  and  indeed 
from  30  to  40  hours.  In  order  to  obtain  a  good  circulation 
in  the  digesters  and  still  avoid  direct  firing,  Koerting,  in 
Hanover,  who  makes  injectors  a  specialty,  has  used  an  in- 


FIG.    46. 

jector  with  a  digester  illustrated  in  Hover's  work,  page 
190.  Figure  46  shows  this  boiler:  B  is  perforated  bottom 
in  the  boiler  A,  which  is  built  cylindrical  with  rounded 


THE    MANUFACTURE    OF    CELLULOSE.  91 

ends.  The  manhole  C,  serves  to  fill  in  the  wood  and  the 
discharging  is  done  by  an  opening  above  the  bottom,  not 
visible  in  the  sketch.  Alongside  the  boiler  is  a  stand-pipe 
F,  which  is  connected  with  the  steam  pipe  D,  and  also  by 
branch  pipes  with  the  lower  and  upper  part  of  the  digester 
which  at  E  are  connected  by  the  well-known  Koerting  in- 
jector. The  steam  coming  to  the  boiler  through  D  draws 
by  means  of  the  injector  E  the  leach  accumulated  under 
the  bottom  B  through  pipe  r,  forces  it  through  the  stand- 
pipe  F  into  the  upper  part  of  the  digester  and  thus  not 
only  effects  proper  heating,,  but  also  a  lively  circulation  of 
the  leach,  which,  after  the  finish  and  after  shutting  off 
the  steam  supply  is  let  off  through  the  pipe  s. 

For  starting  and  maintaining  the  circulation  of  the  leach 
it  is  only  necessary  that  the  pressure  of  the  steam  supply 
be  by  one  atmosphere  higher  than  the  pressure  in  the  di- 
gester. To  regulate  these  conditions  of  pressure,  which 
can  be  observed  by  a  manometer  M,  a  safety  valve  is  ar- 
ranged at  C,  which  is  weighted  in  proportion  to  the  press- 
ure required  in  the  digester. 

The  system  of  lingerer  in  Vienna,  already  mentioned  as 
the  most  rational  soda  process  for  the  best  utilization  of 
the  leach,  is  described  in  regard  to  the  digesting  process 
by  Hoyer  as  follows:  The  method  is  based  on  the  prin- 
ciple of  displacement  and  the  work  is  done  in  such  man- 
ner that  the  leach  in  certain  order  passes  a  number  of  di- 
gesters (Battery),  which  are  heated  by  steam  and  charged 
with  wood  cut  into  thin  slices.  A  battery  consists  of  7 
to  10  upright,  fixed  digesters,  which  by  pipes  and  valves 
are  connected  in  such  manner  that  steam  or  leach  can  be 
let  from  one  boiler  into  another,  as  directed.  With  this 
system  of  digesters  the  work  is  so  carried  on  that  fresh 
wood,  with  the  substances  easiest  dissolved,  is  first  treated 
with  steam  which  comes  from  the  digester  which  is  ready 
to  be  discharged,  and  then  with  leach  weakest  in  soda,  be- 
cause richest  in  extractive  matter,  which  comes  from  the 
digester,  which  was  most  recently  charged  with  fresh 
wood,  and  has,  therefore,  passed  all  the  other  digesters 
and  has  started  circulation  with  the  boiler  from  which  the 
wood  is  next  to  be  discharged.  If,  for  instance,  the  battery 
consists  of  seven  boilers,  A.  B.  C.  D.  E.  F,  Gr,  in  working, 
the  leach  is  changed  about  as  follows:  When,  for  instance, 
C  has  been  newly  filled  and  B  is  to  be  discharged,  steam  is 


92  THE    MANUFACTURE    OF    CELLULOSE. 

first  let  from  B  into  C  to  steam  the  fresh  wood,  the  weak- 
est leach  is  then  run  from  D  to  C  and  so  in  succession;  al- 
ways stronger,  from  E  to  D,  from  F  to  E,  from  G  to  F.  from ' 
A  to  G  and  from  .B  to  A.  After  about  one  hour  the  leach 
is  let  off  from  C,  to  be  regenerated,  while  immediately 
after  this  discharge  an  advancing  of  the  leach  D  to  C 
etc.,  takes  place,  and  A  is  charged  with  fresh,,  pure  leach. 
In  this  manner  every  hour  one  digester  is  ready  for  dis- 
charge and  its  charge  is  washed  with  hot  water  under 
steam  pressure,  before  being  emptied.  In  the  same  degree 
in  which  the  leach  in  its  circulation  becomes  weakened, 
also  the  temperature  and  the  steam  pressure  can  decrease, 
which  in  this  process,  in  which  the  leach  by  the  contin- 
uous change  comes  to  effect  under  the  most  favorable  cir- 
cumstances is  in  the  digester,  charged  with  fresh  leach, 
not  more  than  about  6  to  8  atmospheres  for  pine  and  3  to 
4  atmospheres  for  leaved  wood.  The  fresh  leach  contains 
for  pine  wood  from  5  to  6  per  cent,  for  leaved  wood  from 
3  to  4  per  cent  soda.  The  leach  saturated  with  the  ex- 
tractive matter  and  incrusts  from  the  last  digestation  is 
then  by  evaporation  and  calcination  always  recovered 
again  for  the  process,  so  that  according  to  the  statements 
by  the  inventor,  for  100  kilo  dry  cellulose  but  5-6  kilo  of 
soda  get  lost.  According  to  age,  growth  and  kind  of  the 
wood  used,  1  volumeter  wood  yields  from  100  to  120  kilo 
cellulose  for  pine  wood  and  somewhat  more  for  leaved 
wood  (150  to  180  kilo).  Further  for  1  volumeter  wood 
about  60  kilo  soda  of  90  per  cent  are  estimated  for  con- 
version into  caustic  soda,  of  which  0.9  are  recovered  by 
regeneration. 

B.  SULPHITE  PKOCESS. 

The  boilers,  which  are  used  in  the  sulphite  process  and 
especially  in  the  Mitscherlich  process,  first  to  be  treated, 
differ  from  the  previously  described  considerably,  be- 
cause on  the  inside,  like  all  parts  connected  with  it, 
they  must  be  protected  against  the  corrosive  action  of  the 
sulphurous  acid.  Besides  as  the  digesting  process,  accord- 
ing to  Mitscherlich,  requires  much  more  time,  it  is  a  mat- 
ter of  consequence  to  arrive  at  boiling  at  omce  as  much 
wood  as  possible,  i.  e.,  to  make  the  digesters,  very  large. 
Certainly  not  all  factories  working  according  to  Mitscher- 
lich, have  horizontal  boilers;  some  also  have  upright,  of 


THE    MANUFACTURE    OP    CELLULOSE. 


92 


somewhat  smaller  dimensions,  most,  however,  have  the 
horizontal  digesters  of  4  meter  inside  diameter  and  12 
meter  length,  which  hold  the  enormous  quantity  of  a  100 
cubic-meters  of  cut  wood  and  still  have  to  take  60  cubic- 
meters  of  leach.  With  such  dimensions  it  becomes  neces- 
sary to  use  very  heavy  metal,  at  least  18  millimeter  (at  the 
half  rounded  heads  still  stronger)  and  also  to  consider  the 
expansion  of  such  iron  masses  in  heating.  In  fig.  47  and 
48  it  can  be  seen  that  the  foundation  of  the  digesters  is 


s 


formed  by  two  strong  walls,  over  which  5  strong  beams  are 


94  THE    MANUFACTURE    OF    CELLULOSE. 

laid;  the  digester  has  rivited  to  itself  five  cast  iron  feet, 
which  rest  on  these  beams,  but  not  immediately.,  as  short 
iron  rollers  are  between  the  feet  and  the  beams,  which 
eventually  permit  some  expansion  of  the  long  'digester. 
Two  manholes  on  top,  which  by  easily  loosened  screws  caii 
be  tightly  closed  (the  packing  is  done  with  rings  of  lead 
and  by  means  of  a  paste  of  cellulose)  permit  filling  from 
two  sides  at  the  same  time  and  two  oppositely  arranged 
manholes  below  are  for  discharging,  whereby  after  finish- 
ing the  operation  all  four  opened  manholes  let  the  air  pass 
through  and  make-  thus  some  cooling  off  possible.  It  may 
here  be  mentioned,  that  the  foundation  walls  must  be 
above  man  high,  so  that  the  space  formed  under  the  di- 
gester, which  is  connected  and  arranged  for  draining  off, 
will  be  large  enough  to  easily  hold  the  whole  charge  of  the 
digester.  The  digester  itself  is  filled  as  follows: 
At  one  upper  end  is  a  main-valve  to  shut  off  the  digester 
during  the  operation,  and  a  cross-nipple,  carrying  four  oth- 
er valves:  of  these  a  is  connected  with  the  boiler,  b  with  a 
water  pump  or  a  reservoir,  c  with  the  leach  tank^  and  d 
with  the  drive-over-tower.  At  the  opposite  tower  end  is 
the  discharge  value  e  and  besides  in  the  middle  of  each 
head  a  nipple  leading  inside:,  carrying  an  angle  thermom- 
eter and  a  manometer,  also  a  small  cock,  by  which  during 
the  operation  some  leach  can  be  drawn  and  indirectly  the 
process  and  its  finish  can  be  observed  and  determined. 
Either  also  in  a  head,  or  at  the  sidewalk,  four  more  nipples 
are  arranged  next  to  each  other,  through  which  the  heat- 
ing pipes  enter  the  inside,  each  of  which  can  be  shut  off 
by  a  valve  (f,  g,  h,  i). 

Because  in  the  Mitscherlich  process,  as  mentioned,  the 
boiling  operation  takes  much  longer  than  in  the  other 
methods,  the  leach  would  become  too  much,  diluted,  if  the 
steam  were  let  directly  into  the  boiler;  also  the.  tem- 
perature, respecting  the  pressure  in  the  boiler  could  not 
be  as  well  regulated;  therefore  the  heating  of  the  con- 
tents of  the  boiler  is  effected  by  a  system  of  pipes  of  hard 
lead,  which  about  covers  the  lower  third  of  the  total  inside 
wall.  Because  it  often  happens,  that  a  pipe  bursts  during 
work  and  has  to  be  shut  out,  for  precaution  four  pipes 
were  laid  alongside,  which  have  a  total  length  of  about  900 
meters  or  more.  The  four  pipe  systems,  which  lay  in  four 
coils  close  to  each  other,  pass  out  again  at  the  opposite  end 


THE    MANUFACTURE    OP    CELLULOSE.  95 

of  the  digester  and  every  system  can  be  shut  off  inde- 
pendently by  a  valve.  This  is  necessary,  because,  as  already 
mentioned,  a  pipe  sometimes  bursts  inside  while  working. 
When  then  in  this  coil  the  steam  has  been  shut  off,  the 
leach  enters  through  the  leak  into  this  pipe  and  through 
it  gets  outside;  in  such  case  the  leak  can  be  noticed  by  a 
strong  smell  in  the  room,  and  closing  both  valves  the  pipe 
system  concerned  can  be  completely  shut  out.  By  this 
the  duration  of  an  operation  is  certainly  somewhat  pro- 
longed, but  the  loss  of  leach  and  injury  by  the  escaping 
sulphurous  acid  are  presented;  the  process  can  go  on  with- 
out delay. 

The  repeatedly  mentioned  protection  of  the  iron  digest- 
ers is  effected  as  follows:  The  inside  well  cleaned  digester 
is  first  coated  with  a  mixture  of  tar  and  pitch,  and  on  top 
of  this  very  thin  sheets  of  lead,  so  called  lead  foil,  about 
1-8  millimeter  thick,  are  pasted  in  single  sheets,  sheet  by 
sheet,  so  that  the  sheets  are  well  pressed  into  all  cavities 
and  corners,  but  without  tearing  them.  The  lining  is, 
however,  done  piece  by  piece,  and  only  as  far,  as  the 
brick  lining  is  about  to  be  laid,  which  is  provided  to  form 
the  main  protection.  For  this  purpose  it  is  necessary  to  select 
quite  hard,  porous,  acid  proof,  hard  burned  stones  of  the 
form  and  size  of  the  common  brick,  but  which  are  made 
with  tongue  and  groove,  in  order  to  be  abl#  to  make 
a  joint  as  close  as  possible.  Because  it  is  not  so  much  the 
liquid  leach,  which  acts  destructively,  as  the  gaseous  sul- 
phurous acid,  evolved  in  the  upper  part  of  the  digester, 
it  is  most  important  to  protect  mainly  the  upper  half  of  the 
digester;  it  is  therefore  sufficient,  when  the  lower  half  of 
the  boiler  is  well  covered  with  two  flat  layers  of  brick, 
while  the  upper  as  a  rule  consists  of  two*  vaults,  each  25 
centimeters  thick,  one  spanned  over  the  other,  consequent- 
ly of  two  roll  layers.  For  binding,  best  Portland  cement, 
mixed  with  some  sand,  is  used.  The  whole  wall,  especial- 
ly the  connection  to  the  manholes,  the  sides  of  which 
must  be  protected  by  several  heavy  sheets  of  lead,  must  be 
made  very  carefully,  because  otherwise  a  new  digester 
would,  be  completely  eaten  up  in  a  short  time.  The  sul- 
phurous acid  gas  under  pressure  eats  through  very  quick- 
ly, indeed,  when  there  is  but  one  defect  joint.  For  this 
reason  it  was  tried  to  limit  the  number  of  joints  to  a 
minimum  and  lately  instead  of  the  brick  form,  plates  were 


OS  THE    MANUFACTURE    OF    CELLULOSE. 

chosen  and  to  make  the  different  joints  as  thin  as  possible, 
the  form  of  these  plates  has  been  exactly  suited  to  the 
shape  of  the  digester,  which  especially  at  the  round  heads 
is  of  great  importance.  At  the  same  time,  in  used  burned 
plates,  which  are  certainly  much  thinner  than  the  bricks, 
the  advantage  has  been  gained,  that  the  hold  of  the  boiler 
becomes  considerable  larger  and  the  weight  of  the  ap- 
paratus somewhat  smaller.  At  this  point  it  may  be  men- 
tioned that  in  lining  the  boiler,  it  can  scarcely  be  prevent- 
ed that  the  thin  lead  foil  in  some  places  gets  damaged;  by 
this  the  so  necessary  protection  is  partially  missing.  For 
this  reason,  lately  sheet  lead,  3  millimeters  thick,  in  rolls, 
as  large  and  wide  as  possible,  is  employed.  These  are 
soldered  together  inside  (whereby  naturally  the  boiler  has 
to  be  turned),  so  that  a  perfect  lead  lining  protectingly 
covers  the  sheet  iron.  On  account  of  the  weight  of  the 
lining  alone  it  is  necessary  to  connect  the  lead  to  the  wall 
of  the  digester  with  screws  with  large  heads  and  then  to 
cover  these  heads  again  with  plates  of  lead,  soldered  over. 
In  selecting  the  sheet  lead  care  must  be  taken  to  use  but 
the  best.  Because  in  change  of  temperature  lead  contracts 
differently  from  sheet  iron,  wrinkles  are  often  formed  in 
it,  its  structure  become  chrystallinic  and  sags.  In  soft  lead, 
when  warping,  it  is  supposed  that  the  pores  open  and  ad- 
mit foreign  substance.  To  make  possible  the  employment 
of  sheets  as  thick  as  possible,  only  thin  sorts  should  be 
taken,  and  of  these  as  many  layers  rolled  together  under 
great  pressure,  as  is  necessary  to  obtain  the  desired  thick- 
ness. 

All  valves,  mentioned  before,  must  certainly  also  be 
lined  with  lead  in  all  their  inner  parts,  as  this  metal  best 
resists  sulphurous  acid.  It  is  also  good  precaution  to  ar- 
range between  steam  boiler  and  digester  a  check-valve,  so 
that  the  leach  never  can  enter  the  boiler,  should  the  pres- 
sure become  less  than  in  the  boiler. 

The  proper  process  of  digestion  comprises  the  follow- 
ing details:  After  the  lower  manholes  were  closed  and  the 
wood  filled  in  through  the  upper  one  and  distributed  as 
uniformly  as  possible  in  the  digester,  the  two  upper  ones 
are  screwed  down,  the  main  valve  is  opened  and  through 
this  valve  steam  is  let  into  the  apparatus;  as.  soon  as  the 
digester  is  all  filled  with  it,  the  outlet  valve  at  the  lower 
end  in  back  of  the  digester  is  opened  and  the  steam  i? 


THE    MANUFACTURE    OF    CELLULOSE.  97 

rushed  through  the  wood  charge  for  about  8  to-  10  hours, 
whereby  care  has  to  be  taken  that  no  pressure  is  produced 
in  the  digester.  The  steam  condensed  on  the  wood  runs 
off  as  a  dark-brown  liquid,  which  smells  like  vanilla,  from 
which  is  clear,  that  already  by  steaming  part  of  the  in- 
crusts  are  dissolved.  But  the  main  object  of  steaming  is 
to  prepare  the  single  pores  of  the  wood  for  admitting  the 
leach.  The  steam  also  displaces  the  air  from  the  inner 
portions  -of  the  wood  slices.  As  soon  as  the  steaming  is 
finished,  the  outlet  valve  closed,  the  steam  supply  shut 
off  and  the  leach  valve  c  is.  opened,  the  cold  leach  streams 
into  the  digester,  the  steam  condenses,  a  vacuum  is  formed 
and  each  smallest  pore  eagerly  draws  in  the  leach,  so  that 
finally  not  only  the  spaces  between  the  wood  are  filled 
with  leach,  but  also  the  wood  itself  is  thoroughly  soaked 
full  with  leach,  like  sponges,  whereby  is  prevented  the 
rising  of  the  wood  above  the  level  of  the  liquid.  In  this 
manner  the  sulphurous  acid  does  not  only  act  dissolvingly 
from  outside,  but  also  out  from  the  inside.  When  the 
digester  is  filled  with  leach,  so  far  that  only  a  small  space 
is  left  at  the  top,  so  that  the  vapor  evolved  in  boiling  has 
room,  the  valve  c  is  closed  and  after  all  packings  are  tightly 
screwed  down,  the  boiling  itself  is  started,  by  opening  all 
four  steam  valves,  whereby  care  has  to  be  taken  that  the 
pressure  in.  the  steam  boiler  is  the  highest  possible  so  that 
the  digestion  goes  on  energetically  from  the  beginning  and 
the  temperature  from  its  first  state  of  40  to  45°  C  soon 
rises  to  70°,  because  before  that  chemical  action  of  the 
acid  does  not  take  place.  The  valves  at  the  end  of  the 
heating  coils  are  left  open  in  the  start,  that  the  condensed 
water  can  run  off  freely  and  before  steam  comes  out, 
these  are  partially  closed,  and  then  altogether,  when  later 
the  temperature  in  the  digester  rises  too  high.  Thus  the 
coil  is  gradually  filling  with  water  and  it  is  avoided,  that 
the  pressure  in  the  digester  is  larger  than  in  the  coil,  which 
would  be  the  case  when  the  steam  supply  valve  is  closed 
and  the  outlet  valve  left  open.  Formerly  it  had  been  the 
first  principle  with  every  boiling  operation  that  the  pres- 
sure in  the  digester  never  should  exceed  3  atmospheres 
and  the  temperature  should  not  rise  above  114°.  When 
these  limits  were  reached  some  was  driven  over  at  once,  i. 
e.,  part  of  gaseous  sulphurous  acid  in  the  digester  was  let 
off  into  the  "drive-over-tower."  But  competition,  declin- 


THE    MANUFACTURE    OP    CELLULOSE. 


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166  THE    MANUFACTURE    OP    CELLULOSE. 

ing  prices  of  the  cellulose,  and  the  endeavor  caused  thereby 
to  produce  more  and  more  with  the  same  plant,  have  in- 
duced the  manufacturer  to  exceed  these  limits,  not  only 
to  gain  time  in  charging  and  discharging  of  the  digester, 
but  also  to  shorten  the  operation  of  boiling  as  much  as  pos- 
sible.   By  careful  experimenting  the  author  has  found  that 
without  endangering  the  product,  3.4  to  3.5  atmospheres 
and    temperature    as    high    as     120°     Celcius    may    be 
safely     applied.     By     this     whole     period     of     boiling, 
which  formerly  required  75  to  85  hours  (warming  up  in- 
cluded), has  by  and  by  become  reduced  to  58  hours  and 
less,  of  which  but  32  hours  are  required  by  the  process 
proper.     It  must  be  mentioned  in  this  place,  that  the 
kind  of  heating  pipe  system  is  of  much  importance  in  re- 
gard to  the  d-uration  of  the  process,  as  the  length  of  the 
pipes,  the  strength  of  its  walls,  keeping  it  free  of  de- 
posits of  sulphate  of  lime,  all  have  an  effect  in  hastening 
or  delaying  the  delivery  of  heat,  and  also  the  digesting. 
It  is  well  to  take  care  that  neither  pressure  nor  temperature 
go  down  before  the  operation  is  finished,  but  be  kept  uni- 
formly high,  as  much  as  possible,  at  least  towards  the  end. 
This  certainly  requires  sharp  control.     To  give  a  clear 
illustration  of  the  run  of  the  digesting  process  in  its  differ- 
ent stages  and  at  the  same  time  to  get  acquainted  with  the 
time  necessary  between  the  charges,  examples  from  practice 
are  given  on  the  preceding  page  which  contain  the  notes 
about  any  operations  as  written  down  for  control  in  the  so- 
clled  "boiling-book"  of  every  cellulose  factory. 

Examining  and  comparing  these  three  examples  it  can 
be  clearly  seen  that  the  warming  up  until  the  beginning 
of  the  digesting  process  requires  from  18  to  28  hours 
time  and  that  the  prosper  digestation  in  these  three  ex- 
amples takes  almost  equally  long,  i.  e.,  31.5,  35  and  37 
hours.  The  previous  steaming  has  required  8,  10  and  12 
hours  time.  The  charging  of  wood  and  acid  was  also  vary- 
ing according  to  local  conditions.  Including  these  manipu- 
lations; from  charging  to  blowing  off  were  required1,  in 
the  first  factory  80-J  hours,  in  the  second  87  hours,  and  in 
the  third  72  hours.  To  this  time  has  to  be  added  the  blow- 
ing off,  letting  off  the  leach,  cooling  off  and  washing,  also 
discharging  and  revision  of  the  boiler,  to  be  done  any 
time,  which  labors  require  at  least  18  to  24  hours,  so  that 
for  the  total  duration  of  one  operation  90  to  100  hours 


THE    MANUFACTURE    OF    CELLULOSE.  101 

have  to  be  calculated,  consequently  only  7  to  8  operations 
can  be  made  per  month  with  one  digester. 

When  employing  sufficiently  strong  leaches,  i.  e.,  rich 
in  free  sulphurous  acid,  when  other  circumstances  are  fa- 
vorable, especially  in  larger  works,  with  Mitscherlich  boil- 
ers 11  to  12  operations  may  be  made  per  month,  but  the 
leach  must  contain  about  two  parts  free  sulphurous  acid 
for  one  part  combined. 

In  regard  to  the  controlling  of  the  process  and  especial- 
ly determining  its  end,  this  can  be  done  only  by  drawing 
from  the  stop-cock  at  the  gauge-nipple  some  of  the  leach 
and  testing  it.     For  this  purpose  a  200  mm.  test  tube  is 
filled  to  about  60  mm.  with  commercial  ammonia  solution, 
and  holding  the  tube  with  a  clamp,  some  of  the  hot  leach 
from  the  stop^-cock  is  added  and  then  the  liquids  well 
mixed.     The  tube  is  then  set  aside  in  a  test  tube  stand. 
The  ammonia  combines  with  part  of  the  sulphurous  acid 
of  the  bisulphite  of  lime,  whereby  the  resultant  mono- 
sulphite  of  lime  becomes  insoluble,  separates  and  deposits 
at  the  bottom  as  a  white  powder.     The  higher  this  layer 
of  precipitate  is  the  more  bisulphite  of  lime  is  contained 
in  the  leach  therefore  the  less  it    has    been    used    up. 
Because  in  practice  the  duration  of  each  operation  is  al- 
most the  same,  it  is  sufficient,  when  beginning,  to  take 
samples  in  the  second  half  of  the  process,  from  time  to 
time.    But  the  less  the  precipitate  appears  the  oftener  the 
tests  must  be  made;  towards  the  end  this  should  be  done 
every  quarter  of  an  hour,  as  the  precipitate  must  not  be 
allowed  to  entirely  disappear.     The  nearer  the  end  the 
quicker  and  coarser  the  precipitate;  its  color  becomes  yel- 
lowish, and  smell  changes,  is  not  a  pungent,  and  the  liquid 
becomes  sticky  and  darker.    When  the  precipitate  appears 
but  6  to  8  mm.  high,  the  operation  is  finished  and  the  di- 

f  ester  is  blown  off.  After  the  water  is  started  in  the 
rive-over  tower  the  main  valve  of  the  digester  and  valve 
d  are  opened,  so  that  the  gaseous  sulphurous  acid  can  go 
over  to  the  tower  through -a  lead  pipe,  which  for  cooling 
off  is  let  in  a  coil  through  water.  As  soon  as  the  aqueous 
solution  formed  there  reaches  4°B,  it  is  run  off  into  the 
acid- tank.  As  at  times  a  solution  of  from  10-12 °B  is  ob- 
tained, this  blow-off  acid  is  quite  useful  to  the  manufac- 
turer; he  improves  with  it  the  strength  of  a  leach  neces- 
saiy  in  the  next  operation.  As  goon  as  the  pressure  in 


102  THE    MANUFACTURE    OF    CELLULOSE. 

the  digester  has  become  reduced  to  one  and  one-third  of 
an  atmosphere.,  which  tabes  place  in  a  few  hours,  the  dis- 
charge valve  is  opened  and  the  leach,  still  under  some  pres- 
sure, is  let  off  through  a  lead  pipe,  at  least  100  mm.  in 
diameter,  into  the  leach  basin,  about  which  more  will  be 
said  later  on.  When  the  pressure  in  the  digester  is  alto- 
gether reduced  and  the  leach  run  out,  the  discharge  valve 
is  closed  and  the  boiler  filled  through  water  valve  d  to 
about  one-half  with  cold  water,  during  which  manipula- 
tions both  upper  man  holes  are  opened.  Through  these,  by 
means  of  a  pole  and  a  small  arrangement  fixed  to  it,  the 
first  real  sample  of  the  finished  cellulose  can  now  be  taken 
out  to  see  whether  the  operation  was  a  success,  and  ac- 
cordingly to  make  disposition  for  the  further  working  of 
it.  But  in  case  of  a  failure  a  repeated  charging  of  acid 
and  repetition  of  the  boiling  operation  would  not  yield 
a  better  result,  therefore  the  charge  has  to  be  taken  out 
at  all  hazards. 

Letting  in  cold  water  is  mainly  for  the  purpose,  not 
only  to  somewhat  cool  off  the  hot  mass  and  the  digester 
itself,  but  also  to  free  the  material  from  the  brown  leach 
as  quickly  as  possible,  thereby  giving  it  a  preliminary 
washing  or  rather,  rinsing  out.  After  this  first  washing  is 
let  off,  as  second  rinsing  is  done  in  the  same  manner,  but 
then  the  lower  manholes  are  at  once  opened,  and  poles 
are  pushed  through  to  the  upper  manholes,  so  that  a 
draft  through  the  digester  is  secured  and  the  mass  is 
cooling  off  as  much  as  possible. 

As  soon  as  it  can  be  done,  two  persons,  mouth  and 
nose  covered  with  sponges,  must  go  into  the  digester  and 
commence  discharging  with  wooden  shovels  and  picks. 
This  on  account  of  the  strong  smell  and  great  heat  still 
prevailing  in  the  apparatus  is  not  easy  work:  the  labor- 
ers must  often  shift  and  naturally,  the  labor  of  discharg- 
ing, done  by  contract,  must  be  well  paid  for.  This  work, 
however,  is  not  really  injurious  to  the  health  of  the  la- 
borer, as  men  who  were  at  it  for  years  never  showed  any 
symptoms  of  sickness. 

Not  only  for  the  Mitscherlich  system,  but  for  all  other 
processes  a  method  has  lately  been  recommended  to  re- 
move the  sulphurous  acid  as  much  as  possible  before  the 
stuff  leaves  the  digester.  This  is  the  method  of  Carpen- 
ter and  Schulze,  in  Berlin,  heating  the  leaches  after  fin- 


THE    MANUFACTURE    OF    CELLULOSE.  102 

ishing  the  operation  of  digestation,  by  driving  compresed 
and  heated  air  by  a  blower  through  a  perforated  pipe 
into  the  boiled  mass,  whereby  the  stuff  becomes  fibered 
and  at  the  same  time  are  formed  resulting  combinations 
which  otherwise  do  not  form  before  draining,  after  leaving 
the  digester,  under  the  influence  of  atmospheric  air.  In 
the  upper  part  of  the  boiler  is  another  perforated  pipe, 
through  which  air  and  sulphurous  acid  can  be  drawn  off. 

When  the  cellulose  is  removed  from  the  digester,  and 
the  boiler  is  swept,  if  necessary,  the  heating  pipes  are  then 
knocked  with  wooden  hammers  to  remove  the  sulphate, 
often  depositing  on  the  pipes  in  considerable  thickness, 
because  as  a  poor  conductor  of  heat  it  very  much  injures 
the  heating  capacity. 

Every  single  pipe  system  must  be  separately  tested  to 
see  whether  it  is  tight,  does  not  let  through  steam,  and 
also,  whether  by  leach  having  entered  and  formed  sulphate 
(gypsum)  inside,  it  has  not  become  stopped  up.  In  the 
first  case  the  leak  must  be  corked  or  a  new  piece  of  lead- 
pipe  must  be  set  in,  which  can  be  rapidly  accomplished,  if 
the  pipe  pieces  are  not  soldered  but  screwed  together 
with  bronze  flanges.  When  the  pipes  are  stopped  up,  mur- 
iatic acid  is  filled  in  and  slowly  driven  through  with  a 
little  pressure  of  steam,  finally  after  every  operation  the 
whole  lining  must  be  well  looked  over,  especially  the  top. 
The  heat  prevailing  inside  soon  dries  up  the  face  of  the 
wall  completely  except  at  the  spots  where  the  acid  has 
penetrated  the  joints  where  it  trickles  out  again  as  moist- 
ure and  thus  shows  plainly,  where  it  is  most  necessary 
to  do  the  joints  over.  If  this  important  matter  is  -neg- 
lected the  complete  destruction  of  the  digester  will  soon 
be  caused.  The  saving  of  time  at  this  point  can  therefore 
not  be  recommended. 

In  regard  to  using  hard  leacl  for  heating  pipes,  it  must 
be  finally  remarked  that  it  is  followed  by  a  number  of  in- 
conveniences which  long  ago  made  desirable  a  substitute, 
and  finally  led  to  the  use  of  copper,  the  resistance  of  which 
against  sulphurous  acid  was  not  regarded  with  much  favor. 
On  account  of  its  greater  power  of  resistance  the  hard 
lead  pipes  were  first  chosen,  which  in  consequence  of  the 
steam  going  through  under  pressure  in  long  coils,  have 
to  stand  greater  differences  of  temperature.  But  for  that 
lead  is  very  little  suited.  Being  an  imperfectly  elastic 


104  THE    MANUFACTURE    OF    CEOJLULOSE. 

body,  it  does  not  contract  to  its  original  form,  when  on  ac- 
count of  previous  raising  of  temperature  it  had  suffered 
expansion.  Moreover  there  are  occasionally  stronger  an4 
weaker  layers,  bends,  which  in  pipes  becomes  suspicious 
as  constrictions  and  dilations,  also  cracks,  through  which 
leach  and  stuff  are  entering  and  causing  partial  or  total 
stopping  up.  All  these  influence  the  heating  effect  and 
prolong  the  duration  of  an  operation.  This  is  still  exag- 
gerated by  the  layer  of  separated  lime  salts,  deposited 
around  the  heating  pipes.,  being  a  poor  conductor  of  heat, 
and  which  cannot  be  as  quickly  and  thoroughly  removed 
from  the  soft  metal  which  is  easily  injured.  Lead  is  in 
itself  little  suited  for  heating  pipes,  because  it  is  not  a 
good  conductor  of  heat,  and  the  pipes,  in  order  to  be 
durable,  must  be  of  considerable  thickness.  Not  one  or  all 
these  disadvantages  however  is  met  with  in  copper.  Cop- 
per pipes,  by  virtue  of  the  great  firmness  of  this  metal, 
can  be  made  quite  thin,  at  a  thickness  of  wall  of  from 
3  to  4  mm.,  and  besides  copper  is  an  excellent  conductor 
of  heat.  Changes  of  temperature  do  not  cause  the  bad 
effects,  as  with  lead,  and  the  coil  does  not  form  one  single 
stiffness,  but  is  composed  of  a  number  of  sections,  4  to  5 
meters  long,  connected  by  couplings  of  acid  proof  bronze, 
which  at  any  place  may  be  exchanged  at  pleasure.  The 
resisting  capacity  of  copper  against  sulphite  leach  has 
proved  to  be  greater,  as  in  the  first  operation  it  gets  cov- 
ered with  a  black  coating  of  the  oxydes  of  cop^ 
per,  which  very  likely  is  produced  by  the  action  of  the 
glycose,  present  in  the  leach  and  which  prevents  further 
action.  On  account  of  the  greater  heating  capacity  of  cop- 
per pipes  less  of  them  are  necessary  for  one  boiler,  than 
lead  pipes;  for  the  cubic-meter  volume  about  2.5  meter  of 
pipe.  They  are  varyingly  arranged,  according  to  whether 
they  are  intended  for  horizontal  or  upright  digesters.  In 
the  latter  they  are  run  along  side  the  wall,  in  the  former 
at  the  lower  side  in  coils  measuring  about  1-5  of  the  wall 
and)  the  water  of  condensation  is  removed  by  suitably 
arranged  traps.. 

To  complete  this  treatise  on  heating  pipes,  not  pub- 
lished until  after  the  end  of  1894  in  the  Papier  Zeitung, 
the  author  is  in  the  position  to  state  that  in  1886  he  was 
negotiating  about  the  furnishing  of  copper  pipes  for  a 
Mitscherlich  digester,  with  a  cellulose  factory  in  Steyer- 


THE    MANUFACTURE    OP    CELLULOSE.  105 

mark,  which  already  in  1885  or  earlier  has  furnished  such 
pipe  systems  to  other  factories,,  which  were  very  well  sat- 
isfied with  its  work. 

An  operation  as  described  above,  yields  about  10,000 
kilos  of  finished  dry  cellulose  and  according  to  several  ex- 
periments by  the  author  for  100  kilos  cellulose  about 
0,956  volumeters  or  0.62  cubic  meters  of  wood  (pine) 
are  needed  on  the  average,  which  is  exactly  accordant 
with  Mitscherlich's  statements,  who  calculates  0.63  cubic 
meters  of  wood  for  100  kilos  of  cellulose.  At  this  the  relation 
between  testmeter  and  volumeter  is  not,  as  generally  stat- 
ed in  books,  accepted  7:10,  but  65:100,  which  latter  fig- 
ures have  become  fixed  by  practice  after  many  trials. 

Every  cellulose  factory,  according  to  its  working  meth- 
od and  the  kind  of  wood  mainly  used,  will  certainly,  in 
regard  to  the  average  yield  in  cellulose,  obtain  a  percen- 
tage number,  somewhat  differing;  from  the  results  of 
other  factories.  So  for  instance,  according  to  an  older 
publication  at  the  Weissenborn  factory  they  figure  2,400 
kilos  cellulose  for  12  testmeter,  consequently  200  kilos  for 
1  testmeter  and  140  kilos  for  I  volumeter.  This  result 
can,  on  account  of  being  so  high,  be  accepted  as  correct 
only  for  very  good  and  barked  material.  The  specific 
gravity  of  the  air  dry  pine  wood  is  0.47,  consequently  1 
testmeter  weighs  470  kilos.  One  cubic  meter,  i.  e.,  one 
volumeter  of  trimmed  pine  wood  weighs  320  kilos,  con- 
sequently 1  volumeter  would  be  0.68  or  about  0.7  test- 
meter,  which  however,  is  somewhat  too  high,  according 
to  the  author's  experience.  The  difference  is  by  no 
means  unimportant,  because  as  a  rule,  the  incoming  wo:d 
is  piled  up  and  accepted  per  volumeters,  but  figured  and 
paid  per  festmeter.  In  the  run  of  the  year  a  considera- 
ble number  of  meters  may  thus  be  paid  over. 

From  the  balance  sheets  of  a  southern  German  factory 
it  is  learned  that  per  cubic  meter  pine  would  equal  156 
kilo  air  dry  cellulose. 

A  northern  German  factory  worked  up  in  one  year 
52.10  volumeters  of  wood  and  produced  in  the  same 
period  715,000  kilos  of  stuff  at  large  (I.  II,  III,)  conse- 
quently 1  volumeter  would  yield  137  kilos  air  dry  cellu- 
lose, which  keeps  the  middle  between  the  above  men- 
tioned figures. 

The   cellulose   factory   Waldhof,   before    its   new   plant 


106  THE    MANUFACTURE    OF    CELLULOSE. 

was  started,  had  a  daily  production  of  1,400  centner  dry. 
The  consume  of  wood  amounted  to  170,000  testmeters  per 
year.  The  yield  of  cellulose,  amounting  to  25,000,000  kilos 
per  year  it  follows,  that  for  1  testmeter  148  kilos  must  be 
figured,  or  for  1  volumeter  104  kilos  of  cellulose.  Sup- 
posing now,  that  these  104  kilos  of  cellulose  were  ob- 
tained from  1  volumeter  embarked,  equal  to  0.8  volumeter 
of  barked  wood,  the  yield  from  a  full  volumeter  of 
barked,  good  wood  amounts  to  130  kilos  of  cellulose, 


s 


j£ 


Fig.  49. 

which  does  not  differ  much  from  the  Weissenborn  result. 
About  the  proper  occurrence  inside  of  the  digester,  dur- 
ing the  process  of  digestion  up  to  the  present  com- 
paratively few  observations  have  been  made.  A.  Herr  Nils 
Pedersen  has  in  No.  19  and  34  set  1890  of  the  Papier 
Zeitung  published  quite  interesting  researches,  which  in 
this  volume,  serving  more  practical  purposes,  could  not 
be  together  admitted.  Only  the  final  results  of  the  inves- 


THE    MANUFACTURE    OF    CELLULOSE.  107 

tigations  about  leaches,  which  were  taken  in  certain  in- 
stances during  the  operation,  shall  here  be  regarded  as  the 
figures  obtained  were  used  in  a  graphical  description,  which 
gives  a  plain  picture  of  the  decomposition  of  the  wood 
in  the  digester.  In  both  figures,  at  the  base  are  marked 
horizontally  the  hours  required  by  the  process,  after  the 
temperature  in  the  digester  had  reached  105°;  the  ordi- 
nates,  i.  e.,  the  verti  car  lines  give  the  per  centage;  the 


Pig.  50. 

temperatures  of  the  digester  at  the  different  times  are 
marked  at  the  upper  horizontal  line. 

Curve  I  shows  how  the  sulphurous  acid  gradually  is 
forming  combinations  with  the  organic  constituents. 
Curve  II  shows  how  the  organic  constituents  are  accumu- 
lating in  the  course  of  time,  expressed  in  per  cent. 

Curve  III  shows  how  the  loose  combinations  first  are 
continuously  forming,  up  to  a  point  from  where  the  curve 
descends,  consequently  decomposition  is  commencing. 


108  THE    MANUFACTURE    OF    CELLULOSE. 

In  serving  an  explanation  to  this,  the  investigations 
have  proved  that  in  the  leach  part  of  the  sulphurous 
acid  is  existing  in  a  loose  combination,  which  is  decom- 
posed by  boiling.  By  adding  a  stronger  acid,  for  in- 
stance, sulphuric  acid,  the  decomposition  -ensues  still 
easier.  The  same  observation  was  made  by  the  author 
years  ago,  when,  for  the  purpose  of  rendering  the  leach 
inoffensive  it  was  evaporated  in  large  open  vessels  and 
for  the  more  rapid  driving  off  of  the  sulphurous  acid,  sul- 
phuric a,eid  was  adlded  with  success.. 

The  curve  indicating  the  organic  constituents  is  as- 
cending in  almost  a  straight  line,  in  the  beginning  so  also 
is  the  sulphurous  acid.  But  it  is  remarkable  that  where 
the  loose  combinations  are  beginning  to  get  decomposed 
the  curve  of  the  sulphurous  acid  does  not  ascend  as  rapid- 
ly as  before,  because  here  not  only  the  free  sulphurous 
acid  is  acting  on  the  organic  constituents,  but  also  the 
sulphurous  acid,  split  off  the  loose  combinations,  but  aU 
ready  counted  in  once,  as  combined  with  organic  con- 
stituents. 

In  the  second  figure  the  results  of  the  analysis  of  a  sec- 
ond leach,  richer  in  lime,  are  entered,  just  as  before  and 
for  better  comparison,  the  curves  of  the  first  figure  are 
here  repeated  in  dotted  lines.  Curve  I  reprsents  both  loose 
combinations  together.  As  appearing  from  the  illustra- 
tion, also  the  two  other  curves  deviate  very  little. 

These  researches  by  Mr.  Nils  Pendersen,  according  to 
Dr.  Frank's  statement,  were  invited  by  and  built  upon 
preliminary  investigations,  which  he  had  made  sometime 
ago  and  which  he  has  published  already  in  the  year  1888. 

Corresponding  to  the  order  in  the  chapter  about  leach 
making,  the  digesting  process  of  Ritter-Kellner  shall  now 
be  briefly  mentioned  here.  In  this  case  two  upright  boil- 
ers are  used,  lined  with  small  plates  of  lead,  held  to- 
gether by  rings  and  bands  of  lead,,  which  have  two  per- 
forated bottoms,  between  which  the  wood  is  filled  in.  The 
digesters  are  connected  by  pipes  in  the  manner  shown  in 
Fig.  51,  taken  from  the  letter  of  patent.  A  and  B  are 
two  iron  vessels  with  inside  lead  lining,  vessel  C  con- 
tains the  solution  of  sulphurous  acid,  Cl  fresh  water.  A 
pipe  1  leads  from  C  to  Cl  by  branches  2  and  3  with  regu- 
lating valves  5  and  6  into  both  digesters  and  enters  a  lit- 
tle above  the  grates  a  and  b,  which  keep  the  wood  immerg- 


THE    MANUFACTURE    OF    CELLULOSE. 


109 


ed  into  the  liquid.  The  pipe  4  is  tothe  right  communicating 
with  a  steam  boiler  and  a  vessel  with  sulphurous  acid.  Pipe 
4,  which  to  the  left  at  c  ends  into  the  gutter  cl,  has  two 
branches  7  and  8,  which  enter  the  bottom  of  the  boil- 
ers, where  they  are  closed  with  regulating  valves  9  and.  10. 
Besides  pipe  4  has  two  branches  11  and  12,  with  the  regu- 


...ft-. 


Fig.  51. 

lating  valves  13  and  14,  and  above  and  into  boilers.  To 
discharge  the  digesters,  i.  e.,  to  let  off  the  leadi  the  out- 
lets 17  and  18  are  provided.  The  work  is  carried  on  in 
the  following  manner:  Suppose  boiler  A  to  contain 
wood,  which  is  exposed  to  the  action  of  twice  used  acid 
solution,  while  digester  B  is  filled  with  fresh  wood.  Then 
the  valves  6,  9  and  10  are  opened,  while  5,  13,  14,  15  and 
16  remain  closed';  the  fresh  leach  therefore  runs  through 


110  THE    MANUFACTURE    OF    CELLULOSE. 

pipe  7,  4  and  8  into  digester  B.  When  A  is  filled  with  fresh 
pipe  7,  4  and  8  into  vessel  B.  When  A  is  filled  with  fresh 
leach,  valve  6  is  closed  and  valve  14  opened,  whereupon 
steam  enters  through  the  pipes  7  and  8  into  both  diges- 
ters and  the  W'ood  boils. 

When  the  boiling  is  finished,  valve  16  is  closed  again 
and  valves  14  and  15  are  opened;  the  sulphurous  acid  and 
the  steam  are  blown  through  pipes  12  and  4  into  the  gutter 
c,  or  for  recovery  they  are  regenerated  in  suitable  ap- 
paratuses. Afterward  all  liquid  is  removed  through  out- 
let 18  from  the  digester  B,  in  which  nothing  is  now  con- 
tained but  decomposed  wood.  The  solution  from  digester 
A  by  admitting  fresh  water  from  vessel  Cl  is  then  driven 
into  digester  B  in  the  former  way  and"  is  now  solution 
once  used.  The  operation  is  then  repeated,  thereafter 
the  pipes  2,  11  and  7  shut  off  and  the  digester  A  emptied 
and  again  filled  with  fresh  wood. 

From  there  the  operation  repeats,  only  the  two  di- 
gesters exchange  rolls.  In  place  of  two  digesters,  several 
may  be  employed  at  the  same  time,  whereby  it  would  be 
possible  to  use  the  solution  four  to<  eight  times  and  to 
use  it  up  completely.  The  single  operations  become  then 
considerably  shortened  and  a  product  is  obtained,  excel- 
lent in  every  direction. 

When  especially  white  cellulose  shall  be  made,  the  wood 
is  soaked  with  leach  in  the  digester  and  before  heating, 
by  means  of  a  pump  sulphurous  acid  is  forced  in  until  a 
pressure  of  at  least  two  atmospheres  is  reached.  Not  be- 
fore then  either  steam,  or  steam  mixed  with  sulphurous 
acid  at  a  temperature  above  the  boiling  point  is  let  in, 
until  the  pressure  has  reached  about  fiom  3  to  5  atmos- 
pheres. By  this  in  the  first  state  the  decomposition  of  the 
wood,  in  the  second  the  bleaching  of  the  fibre  is  effected. 
The  stuff  becomes  white,  does  not  contain  any  hard  con- 
stituents and  can  be  further  worked  without  first  pass^ 
ing  a  knot  catcher.  The  boiling  process  requires  about 
14  to  18  hours,  with  low  pressure;  however,  it  may  be  pro- 
longed to  36  hours. 

Dr.  Kellner  amply  describes  his  own  process  of  boiling 
in  set,  1894  page  2586,  as  follows: 

Although  owning  the  first  patents  for  rotating  digester, 
for  the  reason  that  my  first  manufacturing  was  done  with 
such,  I  have,  however,  soon  gone  over  to  the  by  far  more 


THE    MANUFACTURE    OF    CELLULOSE.  Ill 

practical  form  of  the  upright  fixed  cylinder.  My  digest- 
ing apparatus  since  consists  of  an  upright  fixed  cylinder, 
which  on  top  and  below  carries  a  large  manhole!,  fastened 
with  lock-screws. 

This  boiler,  in  the  beginning  of  my  method,  was  lined 
with  sheets  of  lead,  which  were  clinched  to  the  boiler,  or 
soldered  to  strips  of  hard  lead,  which,  in  swallow-tailed 
rabbets  between  the  sheets  of  the  boiler,  where  they  met, 
were  connected  with  the  iron  thermo-chemically.  D.  R. 
P.  34074-1884. 

In  Fig.  52,  for  example,  C  is  the  strip  of  hard  lead,  A 
the  boiler-wall,  B  the  lead  lining,  J  the  clinche  to  connect 
the  boiler  sheets  A  to  A'.  Or  the  lead  sheets  are  with 
easy  fusible  metal  directly  soldered  to  the  digester  walls. 
D.  R.  P.  3725.  As  not  in  every  locality  experienced  lead 
burners  can  be  had,  I  have  tried  from  the  beginning  to  do 
away  with  the  lead  in  the  digester. 


Fig.  52, 

My  first  patent  regarding  this  was  applied  for  in  1887 
by  the  Messrs.  Jung  and  Lindig  to  insure  profound  secrecy, 
and  presented  in  an  altered  condition  two  years  later,  hav- 
ing been  refused  the  first  time.  My  main  object  was  to  ef- 
fect the  double  decomposition  between  the  sodium  silicate 
and  the  icalcium  bisulphite,  at  the  end  of  which  reaction 
sodium  sulphite  and  calcium  silicate  are  formed.  The  lat- 
ter serves  to  close  the  pores  of  the  sulphurous  acid  resisting 
substances  which  are  made  into  a  mass  with  liquid  glass. 
Digesters  coated  in  this  manner  have  proved  to  be  very 
satisfactory,  although  very  .many  factories  have  departed 
from  this  process,  and  returned  to  the  "old  manner  of  lead 
coating. 

In  order  to  prevent  the  lead  from  being  attached,  should 
a  leak  in  any  part  of  the  mass  occur,  I  have  recommended, 
as  illustrated  in  Fig.  53,  to  cover  the  digester  A  with  a 
jacket  B  of  thin  tin  and  to  fill  ihe  interlying  space  with 
the  heavy  residue  obtained  from  the  petroleum  refineries. 

Into  the  outer  jacket  m  enter  the  pipes  m2  and  m3  for 


112 


THE    MANUFACTURE    OF    CELLULOSE. 


m  and,  outlet  of  the  liquid  residues  and  ml  for  emptying. 
In  this  manner  the  boiler  also  receives  heat  from  outside, 
and  forms  at  any  place,  laid  bare  by  cracking  of  the  inner 
lining,  a  protecting  coat  of  mono-sulphite  of  lime.  This 
jacket,  against  the  one  proposed  by  Soloman,  has  the  ad- 


Fig.  53. 

vantage,  that  inside  of  a  few  hours  it  can  be  completely  re- 
moved in  case  of  repairs  becoming  necessary,  and  that 
danger  of  explosion  is  altogether  excluded.  In  the  case 
of  any  rivet  leaking,  the  sulphurous  acid  leaking  out,  es- 
capes through  the  hot  oil  in  the  form  of  gas,  which  is  at 
once  noticed. 


THE    MANUFACTURE    OP    CELLULOSE.  113 

With  digesters,  the  jacket  of  which,  is  heated  with  steam, 
a  dangerous  moment  is  prevalent,  as  the  space  between 
boiler  and  jacket  is  entirely  without  protection  against  sul- 
phurous acid  ,and  therefore  injuries  to  the  inner  digester 
cannot  be  noticed  any  sooner,  than  when  also  the  jacket 
has  become  defective — which  may  cause  deplorable  catas- 
trophes, as  will  be  told  later  on. 

The  heat  required  in  boiling,  I  introduced  by  direct 
steam,  as  I  have  departed  from  indirect  heating  for  the 
reason  that  the  heating  coils  get  rapidly  covered  'with 
mono-sulphite  of  lime,  consequently  do  not  well  con- 
duct the  heat  and  carry  no  end  of  dirt  into  the  stuff.  It 
is  indeed  not  necessary  to  work  with  indirect  steam,  when 
at  liberty,  to-  prepare  the  leach  in  such  concentration,  that 
it  still  has  the  concentration  required  for  boiling,  after 
adding  the  water  of  condensation  from  the  steam.  Such 
was  easy,  because  in  my  leach  making  apparatus  I  can 
produce  leaches  of  to  7.5  °B  without  difficulty,  while  Prof. 
Mitscherlich  could  produce  but  weak  leaches  in  his  towers. 

In  regard  to  the  boiling  itself,  according  to  my  method 
it  is  not  necessary  to  steam  the  wood  previous  to  the  treat- 
ing with  sulphurous  acid,  thereby  diluting  the  latter. 
After  charging  the  boiler  the  leach  is  at  once  let  in  by  a 
pump  through  a  pipe  put  through  the  open  manhole,  in 
such  quantity  and  concentration  that  its  volume  is  so  much 
increased  by  the  water  formed  by  the  condensed  steam 
that  when  a  temperature  of  105 °C  is  reached  the  whole 
of  the  wood  is  covered  with  liquid.  The  concentration  is 
at  the  start  made  high  enough  so  that  after  dilution  with 
the  water  of  condensation  just  that  concentration  results 
with  which  the  boiling  is  desired  to  be  carried  through. 

In  this  manner  at  the  beginning  of  the  period  decom- 
position exactly  the  same  conditions  and  proportions  exist, 
which  are  arrived  at  with  indirect  heating,  but  with 
the  difference  that  much  time  is  saved,  because  by  the  use 
of  large  steam  pipes  a  large  boiler,  producing  about  6,000 
kgr.  stuff,  is  in  1^  hours  brought  to  105  °C,  a  result  which 
with  indirect  heating  requires  several  hours. 

I  then  heat  further  to  about  109  °C,  then  shut  off  the 
steam  and  leave  the  wood  about  3  hours  under  the  influ- 
ence of  the  hot  leach,  so  that  it  can  penerate  every  particle 
of  wood,  before  the  temperature  is  further  raised.  In 
this  manner  I  avoid  all  formation  of  splinters.  This  pause, 


114 


THE    MANUFACTURE    OF    CELLULOSE. 


which  in  my  method  is  called  "stand-still,"  can  be  modified 
according  to  the  nature  of  the  wood  and  its  degree  of  dry- 
ness.  Absolutely  dry  wood  does  not  require  any  stand- 
still, or  less  prolonged  stand-still  than  damp  wood,  be- 
cause the  leach  can  penetrate  quicker  on  account  of  the 
capilarity.  I  then  raise  the  temperature  quickly  up  to  the 
desired  point,  120-138 °C,  again  shut  of  the  steam  and  re- 
peat this  supplying  of  steam  at  regular  intervals. 

To  facilitate  the  entering  of  steam  and  to  eliminate  the 
hydrostatic  pressure  in  the  digester,  I  let  off  from  time  to 
time  through  the  so-called  off-gas-valve  provided  at  the 
upper  neck  of  the  boiler,  some  leach  (sulphurous  acid 
mixed  with  steam)  into  the  condensating-apparatus,  pecu- 
liar to  my  process. 

In  fig.  54  such  condensing  arrangement  is  sketched.  Sul- 


Fig.  54. 

phurous  acid  and  steam  enter  at  a  into  the  lead  pipe  coil  b, 
condense  there,  and  flow  out  at  c  as  liquid  sulphurous 
acid.  The  cool  water  runs  through  pipe  d  into  the  mid- 
dle space  f,  rises  at  the  bottom  between  the  walls  and 
around  the  coil  and  leaves  through  the  over  run  pipe  g. 

During  the  boiling  samples  are  taken  from  time  to  time 
and  these  have  the  following  characteristic  signs:  In  the 
beginning  the  leach  is  wine-yellowish  and  somewhat  tur- 
bulent, then  it  gradually  becomes  darker  and  clearer.  After 
a  few  hours  I  commence  to  test  the  free  sulphurous  acid 
volumetric  with  a  normal  iodine-solution. 

It  is  my  special  discovery  that  the  sulphurous  acid  dur- 
ing the  boiling  does  not,  as  Tilgham  and  others  have  sup- 
posed, becomes  oxydized  into  sulphuric  acid,  but  enters 


THE    MANUFACTURE    OF    CELLULOSE.  115 

in  organic  combinations,  and  forms  organic  sulfinic  com- 
binations. And  my  discovery  it  is  also  that  the  sulphurous 
acid,  keeping  in  this  organic  combinations  does  not  show 
the  iodine  reaction — therefore  the  still  uneombined  sul- 
phurous acid  can  be  estimated  by  titration  with  iodine  dur- 
ing boiling. 

When  making  sulphite-cellulose  I  have  endeavored  to 
produce  a  stuff  giving  general  satisfaction  in  every  way, 
consequently  felting  tough  and  firm  enough  to  bind  wood 
pulp  or  earth  for  ordinary  paper  and  which  at  the  same 
time  shall  be  also  opaque,  soft  and  very  easy  bleachable,  and 
which  could  be  worked  into  finer  and  finest  papers. 

By  my  process  it  is  possible  to  produce  just  as  tough, 
but  there  certainly  is  just  as  difficultly  bleachable  cellu- 
lose, as  by  those  processes,  which  work  with  low  pressure 
and  use  indirect  steam. 

The  reason  why  the  fibre  produced  at  low  pressure  and 
with  direct  steam  is  firmer  is  that  the  inter-cellulose  sub- 
stance, i.  e.,  that  body  which  fills  out  the  capilary  of  the 
fibre,  the  cave  of  the  cell,  has  not  diffused  through  the 
walls  of  the  cells,  because  the  boiling  was  done  under  con- 
ditions which  do  not  permit  diffusion.  Because  when  the 
concentration  of  the  leach  in  an  organic  substance  out- 
side of  the  cells  is  equally  high  with  that  part  which  has 
entered  the  cells  there  is  no  occasion  for  the  latter  to  force 
its  way  through  the  membranes;  if  however,  when  boiling 
with  direct  steam,  the  leach  outside  of  the  cell,  because 
of  the  water  of  condensation,  becomes  diluted,  then  the 
concentrated  solution  contained  in  the  cells  diffuses 
through  the  walls  of  the  cells. 

The  work  is  performed  as  follows: 

TABLE  FOE  BOILING. 
Charging  the  boiler  with  wood .  10  min. 

do  with  tramping  down 30  min. 

Filling  in  leach 20-30  min. 

Making  fast  the  upper  manhole 15  min. 

Steaming  up  to  109°C 1  hour,  30  min. 

Stand-still 3  hours 

Steaming  to  the  desired  temperature ^  hour 

Duration  of  boiling  with  letting  gas  off  leach  and 

several  times  supplying  steam 8-14  hours 

Gasing  off  into  concentration 1  hour 

Blowing  out 15  min. 


116  THE    MANUFACTURE    OP    CELLULOSE. 

Admitting  water  and  discharging 30  min. 

Cleaning  the  digester 1  hour 

Total about  21  hours. 

Therefore,  including  small  repairs  of  the  digestors, 
one  operation  can  be  performed  every  22  to  30  hours. 

Such  repairs  are  reduced  to  a  minimum,  because  besides 
the  manholes,  the  boiler  has  but  one  opening  for  admit- 
ting steam,  one  for  letting  off  leach,  one  for  gasing  oif,  and 
one  to  arrange  a  thermometer  and  stop  cock  for  taking 
samples. 

The  next  described  apparatus  is  designed  to  avoid  losses 
of.  sulphurous  acid  in  boiling,  as  well  as  defiling  the  stuff 
with  precipitates  of  mono-sulphites. 

In  the  sulphite  processes  as  a  rule  the  cold  leach  is  filled 
in  together  with  the  wood,  and  by  inner  or  outer  heating 
gradually  raised  to  the  required  temperature,  at  which 
the  decomposition  of  the  wood  in  its  fibres  takes  place. 
By  this  heating  up  a  considerable  amount  of  mono-sulphite 
of  calcium  is  generally  separating  from  the  leach,  very  likely 
in  consequence  of  a  part  of  sulphurous  acid  being  set  free 
by  the  heating,  and  acts  disadvantageously  in  that  it  forms 
crusts  upon  the  heating  coil  or  upon  the  inner  face  of  the 
digester  walls,  as  also  because  it  discolors  the  stuff,  which 
afterwards  requires  stronger  bleaching.  To  meet  this  dis- 
advantage according  to  the  present  invention  (America  pat- 
ent No.  542,932  and  Austrian  patent  No.  33,685  and  56,- 
889)  the  leach  is  first  heated  outside  of  the  digester  m  a 
special  heater,  whereby  the  separation  of  the  mono-sulphite 
takes  place  outside  of  the  digester  and  is  then  let  over 
by  the  digester  filled  with  wood.  Thereby  the  sulphurous 
acid,  being  set  in  the  heating  of  the  leach,  is  condensed  in 
a  coil-cooler  and  used  again  as  solvent  for  the  separated 
mono-sulphite. 

Fig.  55  shows  a  vertical  cut  of  an  upright  heater  with 
condenser.  It  mainly  consists  of  a  vessel  a  with  steam- 
heating-ooil  b,  into  which  the  steam  enters  at  c,  while 
at  the  end  of  trap  e  is  connected.  Both  above  and  below 
is  also  a  thermometer  t.  Below  at  the  vessel  there  is  an 
outlet  and  cleaning  valve  n.  The  leach  to  be  heated  enters 
(at  f  into  the  vessel  and  leaves  at  g.  On.  top  the  vessel 
is  connected  by  pipe  h  with  the  one  end  j  of  a  coil  con- 
denser, while  the  other  end  jl  leads  to  the  reservoir  for  the 
product  of  condensation.  The  condensor  k  consists  of 


THE    MANUFACTURE    OF    CELLULOSE. 


117 


two  concentric  vessels,  of  which  the  inner  has  openings 
below.  The  condensing  medium  flows  through  pipe  1  in 
the  inner  vessel,  rises  in  the  space  between  the  inner  and 
outer  vessel  and  runs  off  through  pipe  11. 

To  facilitate  the  separation  of  the  mono-sulphite  and 
at  the  same  time  to  keep  it  floating  during  heating,  a 
stirring  arrangement  is  provided  in  the  vessel  (not  repre- 
sented in  the  sketch). 

The  method  proceeds  as  follows:  The  heater  is  filled 
with  leach  and  is  heated  above  the  boiling  point,  with  the 
stirring  arrangement  steadily  going  on.  When  this  point 


Fig.  55. 

is  reached  the  stirring  is  stopped,  the  separated  mono- 
sulphite  permitted  to  settle,  and  the  hot  leach  transported 
to  the  digesters,  already  charged  with  wood.  The  cooled 
gases,  principally  consisting  of  sulphurous  acid  are  liqui- 
fied in  the  condenser  and  let  into  the  storage  tank,  into 
which  are  also  let  the  gases  from  the  digester,  after  finish- 
ing boiling.  After  discharging  and  previous  to  re-charg- 
ing the  heater,  the  liquified  sulphurous  acid  is  let  from 
the  reservoir  into  the  heater,  to  dissolve  the  separated 
mono-sulphite  deposited  at  the  bottom,  when  cold  leach 
is  again  filled  in  and  heating  started  anew. 

Every  process  employed  in  the  manufacture  of  cellu- 
lose and  named  after  its  inventor,  prescribes  for  the  proper 
boiling  of  tile  wood  a  certain  way,  which,  although  in  the 
principle  the  same,  every  different  factory  shows  more  or 


118  THE    MANUFACTURE    OF    CELLULOSE. 

less  variation,  suitable  to  local  conditions,,  the  experience 
of  the  manufacturer  or  manager  and  master  of  boiling, 
the  nature  of  the  wood  worked,  and  other  like  conditions. 
In  the  following  we  describe  some  such  varying  in  par- 
ticulars more  or  less  from  each  other,  but  all  practically 
tried  methods  of  boiling: 

1.  The  digester  is  heated,  the  slower  the  better,  up  to 
116°C,  and  about  2.8  atmospheres,  and  then  the  steam  is 
shu+  off  and  a  stand-still  follows,  which  when  desired  can 
be  extended  to  8  hours.     The  pressure,  at  the  beginning 
of  the  stand-still  rises  somewhat  and  then  gradually  falls 
and  when  necessary,  by  letting  off  steam,  is  brought  down 
to  at  least  2  atmospheres.     Then  follows  renewed  steam 
supply  up  to  the  temperature  of  136°,  4  to  5  atmospheres 
pressure,  and  at  this  the  digester  is  kept,  until  according 
to  looks,  smell  and  strength  of  the  leach  in  sulphurous  acid 
the  boiling  may  be  regarded  finished,  when  the  steam  is 
blown  off  as  quickly  as  possible.       The  duration  of  the 
whole  operation  according  to  this  method  amounts  to  18- 
22  hoi;rs  and  is  principally  suited  for  cellulose  designed 
to  be  bleached. 

2.  The  digester  is  within  about  3  hours  brought  to 
105°  and  then  left  at  stand-still  for  3  hours  more.    After 
that  it  is  blown  off  down  to  3  atmospheres  and  the  heating 
with  steam  continued  until  up  to  125 °C.     Blowing  off 
steam  is  repeated,  until  the  temperature  goes  back  to  120- 
125°  and  then  the  process  is  finished  under  continuous 
supplying  of  steam  in  about  10  to  12  hours  at  130°  C.  Dura- 
tion of  the  operation,  14  to  18  hours. 

3.  Heating  up  to  105  °C  and  2J  to  3  atmospheres  with- 
in 3  to  4  hours,    Then  stand-still,  which  according  to  re- 
quirement and  use  lasts  1  to  3  hours;  then  continuing  heat- 
ing, so  that  at  108°C  about  2£  to  3  atmospheres,  at  115° 
about  3  atmospheres,  at  123°  about  4  atmospheres,  at  130° 
about  4J  atmospheres,  at  135°   about  5  atmospheres  of 
pressure  are  obtained;  the  highest  temperature  permitted 
is  135  to  140°;  if  rising  the  steam-supply  must  be  shut 
off.    Finishing  of  the  operation  at  0.56  to  0.5$  of  sulphur- 
ous acid,  which  should  be  accomplished  in  about  8  to  9 
hours  after  the  stand-still.     Duration  of  operation,  10  to 
14  hours. 

Against  those  mentioned  above,  the  Ritter-Kellner  meth- 
od possesses  the  following  peculiarities  and  advantages: 


THE    MANUFACTURE    OF    CELLULOSE.  119 

1.  The  possibility  of  employing  in  the  dressing  of  the 
wood,  a  diminution  in  the  sulphite  process  as  well  as  in 
the  soda  process  advantages;  first  of  a  uniform  diminution 
and  with  the  consequent  uniform  product,  and  second,  of 
the  rapid  penetration  of  the  particals  of  woo*d  with  the 
leach,  and  consequently  stuff  free  of  splinters;  another  ad- 
vantage is  the  shorter  duration  of  boiling. 

2.  Employment  of  a  leach,  consisting  of  a  double  salt  of 
the    sulphurous    acid:     Calcium-magnesia-bisulphite    and 
produced  by  using  "Dolomit"  in  preparing  the  leach.  The 
advantages  are,  first,  a  less  precipitation  of  lime  in  the  di- 
gester, because  the  monosulphite  of  the  magnesia  is  solu- 
ble in  water  (the  combination  of  lime,  however,  is  decom- 
posed by  the  magnesia  during  boiling)  and,  second,  whiter, 
tougher  stuff,  because  the  sulphurous  acid  is  longer  re- 
tained. 

3.  Employment  of  a  leach   containing  more  then   2 
molecules  of  sulphurous  acid  to  1  of  molecule  of  the  base 
base       (the       composition       of       which        is        conse- 
quently     nearer      to      a      hypothetic      "Trisulphite"). 
The      advantages      are,      first,      the      precipitation    of 
lime     in     the      digester      is      completely      eliminated, 
because  according  to  the  Mariott  law  during  boiling,  the 
molecule  SO2  required  in  the  dissolving  of  Ca  803,  on  ac- 
count of  the  pressure  produced  by  the  S02  in  excess,  can- 
not escape  into  the  vapor  space  of  the  digester;  second, 
the  possibility  to  produce  at  liberty  absolutely  white  and 
cottonlike  cell  stuff,  little  transparent  and  easily  bleach- 
able,  consequently  most  valuable  for  the  manufacture  of 
fine  and  finest  papers. 

4.  The  method  to  submit  the  sulphurous  acid  contain- 
ing gases,  coming  from  the  furnaces,  before  -entering  the 
absorption  apparatus  to  an  energetic  cooling.    The  advan- 
tages are  the  possibility  to  produce  highly  concentrated 
solutions  in  relatively  small  apparatuses,  because  as  well 
known,  the  capacity  for  absorption  (efficient  of  dissolving) 
of  a  liquid  for  gases  increases  with  decreasing  temperature. 

5.  The  method  to  force  these  cold  gases  by  artificial 
pressure  (draft)  through  any  number  of  absorption  ap- 
paratuses.    The  advantages  are,  first,  complete  absorption 
of  the  sulphurous  acid,  consequently  greatest  effect;  sec- 
jnd,  independence  of  air  currents  and  outside  tempera- 
hira;  third,  constantly  uniform  production  in  qualitative 


120  THE    MANUFACTURE    OP    CELLULOSE. 

and  quantitative  respect;  fourth,  no  injuring  of  neighbor- 
ing vegetation;  fifth,  production  of  possible  highly  con- 
centrated leach. 

6.  The  employment   of  upright   cylindrical   digesters 
with  combined  direct  and  indirect,  or  only  direct  heating. 
The  advantages  are,  first,  rapid  boiling,  because  there  is  no 
loss  of  time  by  a  warming  up  of  long  duration;  second,  ex- 
cellent circulation;  third,  no  hard  lime  deposits  at  the  heat- 
ing pipes;  fourth,  convenient  tending  of  the  digester *'and 
rapid  charging  and  discharging. 

7.  Employment  of  rotating  digesters  with  direct  heat- 
ing.   The  advantages  are,  first,  for  smaller  plants  simpler 
attending;  second,  cottonlike  stuff. 

8.  Different  manners  of  lead  lining,  and  the  'employ- 
ment of  water-glass  for  the  production  of  acid-proof  pro- 
tecting mass.     The  advantages  are,  first,  rapid  execution 
of  repairs;  second,  jointless  lining. 

9.  The  lining  of  this  protecting  mass  with  plates  of 
hard  glass.    The  advantages  are,  first,  greater  cleanliness; 
second,  instant  visibility  of  perhaps  occasional  cracks  of 
the  lining  through  the  glass  (as  brown  lime^spots);  third, 
greatest  durability;  fourth,  best  closing  at  the  joints. 

10.  The  method  to  control  the  proceeding  of  boiling 
in  its  progress  by  titration  with  iodine  solution.    The  ad- 
vantages are,  first,  the  possibility  to  exactly  determine  the 
ever  standing  of  the  transformation;  second,  to  be  able  to 
produce  several  qualities,  tough  and  soft,  as  desired. 

11.  Method  to  recover  the  sulphurous  acid  retained  in 
the  digester  after  finishing  boiling,  by  conducting  it  mixed 
with  steam,  through  condensing  coils.  The  advantages  are, 
first,  recovery  of  about  18  to  20  per  cent  of  all  the  sul- 
phurous acid  employed;  second,    no    molestation    of    the 
neighbors;  third,  supply  of  aqueous  sulphurous  acid  for 
the  production  of  possibly  strong  leaches;  fourth,  remov- 
ing of  occuring  sulphate  crusts  in  the  obsorption  appar- 
atuses. 

12.  Method  to  employ  the  sulphite  digester  under  pres- 
sure (blow-off  method).     The  advantages  are,  first,  very 
rapid  discharging,  because  it  is  not  necessary  to  wait  un- 
til the  pressure  has  gone  down;  second,  open  stuff  can  be 
easily  washed  out  and  with  little  water. 

The  other  sulphite  methods,  already  mentioned  in  the 
chapter   of   leach-making,    according   to   Hager,    differ    in 


THE    MANUFACTURE    OF    CELLULOSE.  121 

their  principal  characteristics  of  the  digesting  process  as 
follows : 

Ekman  boils  in^a  cylinder  vessel,  surrounded  by  a  steam 
jacket,  lined  with  lead  and  turning  on  side  pins  for  charg- 
ing and  discharging.  The  digester  about  1.3  meters  wide 
and  4  inches  high  after  being  charged  with  wood  is  filled 
with  the  leach  until  the  wood  weighted  with  perforated 
sheets  of  lead  is  covered  by  it.  By  steam  from  a  separate 
boiler  a  special  over-pressure  is  then  produced  in  the  jacket 
according  to  the  following  rule:  Within  the  first  two  hours 
the  pressure  in  the  inner  vessel  should  be  raised  0.7  atmo- 
spheres, in  the  next  two  hours  about  1.4  atmospheres  per 
hour,  in  the  next  hour  by  one,  and  in  the  two  following  by 
0.7  atmospheres  each.  With  this  final  pressure  of  6  at- 
mospheres the  digester  is  left,  until  a  peculiar  smell  of  the 
vapor  let  out  by  a  valve,  or  a  sample  taken,  indicates  the 
end  of  the  process.  The. steam  is  then  blown  off,  the  liquid 
drained  off  through  a  leaden  strainer  arranged  at  one  end, 
and  finally  after  turning  the  digester  the  contents  are 
dumped,  to  be  washed  or  ground  in  the  ordinary  manner. 
The  product  by  this  method  is  claimed  to  yield  32.68  per 
cent  of  wood  charged  green  or  40  per  cent  of  air  dry  boiling 
wood. 

Francke  in  Molndal  employs  a  horizontal  cylinder  vessel 
of  steel-plate  of  2.2  meters  diameter  and  12.5  meters 
length,  with  a  6  millimeter  strong  lead  lining,  forming  a 
vessel  by  itself,  soldered  together  from  sheets  of  lead, 
which  is  fastened  «to  the  outer  vessel  by  rings  of  brass  in 
distances  of  1  meter.  The  digester,  which  is  slowly  rotat- 
ing (once  in  10  minutes)  and  carries  side  catches  to  lift 
the  wood,  rests  with  wide  flanges  on  rollers,  and  receives 
its  rotation  by  a  worm-movement.  The  digesters  are  first 
filled  to  about  three-fourths  height  with  pieces  of  wood, 
and  then  with  solution  of  from  4  to  50  °B  so  ^that  the 
wood  is  well  covered.  The  boiling  is  effected  at  a  pressure 
of  $bout  3.5  atmospheres,  produced  by  steam,  entering 
through  a  hollow  pin  provided  at  one  end  and  regulated  by 
a  reduction-valve. 

When  the  boiling  has  lasted  about  11  hours,  some  of  the 
mass  is  blown  out  through  a  leaden  cock  for  sample  and 
this  sampling  is  repeated  from  time  to  time,  until  showing 
the  right  quality,  for  which  according  to  quality  and  moist- 
ure of  the  wood  from  12  to  17  hours  are  required.  After 


122  THE    MANUFACTURE    OP    CELLULOSE. 

finishing  boiling  the  gases  and  vapors  contained  in  the 
vessel  under  pressure  are  blown  over  to  the  sulphite  tower, 
to  be  used  again  for  making  new  leach.  Then  the  leach 
is  also  removed  by  letting  it  run  off,  the  boiled  wood  is 
washed  twice  and  finally  dumped  into  drain-boxes.  For 
the  described  operation  for  1,000  kilo  wood,  900  to  1,250 
liters  of  leach  are  necessary. 

In  addition  to  the  above  the  more  detailed  description 
of  the  boiler,  as  taken  from  the  American  patent,  No. 
304,092,  is  given. 

The  boiler,  which  is  not  as  stated  above,  12  meters,  but 
only  about  6  meters  long  by  2  meters  in  diameter,  is  made 
of  tinned  iron  and  provided  with  a  lead  lining.  The  steam 
is  introduced  by  pipes  to  the  right  and  left,  which  in  the 
digester  itself  are  perforated,  so  that  the  steam  can  freely 
steam  into  the  mass.  The  boiler  turns  about  its  long  axis, 
not  in  pin-boxes,  however,  but  upon  rollers.  To  this  pur- 
pose three  heavy  rings  are  arranged  at  the  circumference 
of  the  digester,  each  of  which  rests  on  two  rollers.  The 
turning  of  the  digester  is  accomplished  by  a  worm,  catch- 
ing into  a  worm-wheel  arranged  at  the  circumference. 
The  fastening  of  the  lead  inside  is  done  by  laying  it  loose 
against  the  steel  plates  of  the  digester,  where  it  is  held 
by  straddle-rings.  The  lead  sheets  should  be  as  large  as 
possible,  and  each  should  form  a  complete  ring.  The  joints 
are  soldered  together  and  the  finished  covering  is  then  fast- 
ened to  the  boiler  wall  by  means  of  the  rings  mentioned. 
These  rings  are  split  open  and  can  be  driven  apart  by 
wedges,  whereby  the  bad  is  pressed  close  to  the  walls. 
There  is  an  interlayer  between  lead  and  vessel.  To  be  able 
to  notice  leaks  in  the  lead,  the  jacket  of  the  digester  is 
provided  with  a  great  number  of  holes,  which  can  be  closed 
by  cocks.  The  cocks  are  open  during  working.  If  it  now 
happens  that  the  lead  lining  is  no  more  tight,  the  leach 
will  run  away  at  one  or  more  places  through  the  cocks; 
these  cocks  are  closed  meanwhile  until  the  place  to  be  re- 
paired, which  is  easily  to  be  found  by  the  position  of  the 
cocks  can  be  taken  in  hand. 

These  digesters  have  been  proven  in  practice,  as  have 
also  the  lead  lining,  fastened  by  means  of  the  stradoUe- 
rings  to  be  practical.  To  spare  the  lining,  the  digester 
need  not  rotate  continuously,  but  may  be  put  in  motion 
from  time  to  time,  or  eventually  also  towards  the  end  for 


THE    MANUFACTURE    OF    CELLULOSE.  123 

quicker  discharging.  The  boilers  offer  the  advantage  that 
they  prevent  the  depositing  of  sulphate  of  lime  and  then 
prevent  deterioration  of  part  of  the  stuff. 

The  general  characteristics  of  the  boiling  process  accord- 
ing to  Pictet  and  Brilaz  have  already  been  stated.  There 
remains  to  be  mentioned  only  that  after  boiling  there  are 
contained  in  the  leach  not  only  a  quantity  of  different  sub- 
stances, like  gum,,  resin  and  etherical  oils,  but  also  almost 
all  the  sulphurous  acid,  which  could  be  recovered,  where- 
fore in  this  method  it  is  especially  aimed  to  use  the  leach 
over  again,  by  charging  it  after  the  boiling  operation  into 
a  second  and  also  third  digester,  previously  filled,  with 
wood,  until  it  has  become  saturated  with  other  substances. 
But  as  the  liquid  is  retained  in  the  wood  by  the  power  of 
capilarity,  and  cannot  directly  flow  from  one  digester  into 
another,  the  process  for  this  reason  requires  that  the  wood 
after  discharging  be  pressed  out,  to  recover  the  liquid.  By 
evaporation,  the  sulphurous  acid  is  separated  from  the 
resins,  etc.,  in  solution,  to  be  recovered  by  absorption. 

Regarding  this  apparently  very  simple  method  it  must 
be  remarked  that  the  sulphurous  acid  made  liquid  Nat  10 
to  15°  below  zero,  evolves  a  very  great  pressure,  where- 
from  ensues  the  fact  that  at  a  temperature  of  85  °C  in  the 
boiler  there  is  already  prevailing  a  pressure  of  7  atmos- 
pheres, notwithstanding  the  considerable  dilution  of  the 
sulphurous  acid,  because  at  this  temperature  only  very 
small  quantities  of  the  sulphurous  acid  are  dissolved  in 
the  water.  As  it  is  very  difficult  to  exactly  regulate  the 
low  temperatures  this  simple  method  offers  considerable 
danger  on  account  of  the  high  pressures  produced  as  soon 
as  the  temperature  is  slightly  raised. 

Besides  must  be  remarked  that  in  this  process  part  of 
the  sulphurous  acid  becomes  oxidized  at  higher  temper- 
ature, thus  blackening  the  wood  substances,  the  more  as 
in  the  leaches  the  protecting  lime  is  missing;,  which  in  other 
method,  existing  as  monosulphite  of  lime,  gives  off  the 
sulphurous  acid  and  absorbs  and  neutralizes  the  sul- 
phuric acid  formed. 

Flodquist  employs  a  revolving  spherical  boiler  of  steel 
plates,  lined  inside  with  lead,  which  are  fastened  with 
screws  having  large  flat  heads,  plated  with  lead.  Besides 
the  steel  plates  have  a  number  of  small  holes,  through 
which  the  air  can  escape  when  pressing  against  them. 


124  THE    MANUFACTURE    OP    CELLULOSE. 

After  the  boiler  is  charged  and  fed  with  leach  of  5°B  it  is 
heated  by  steam,  so.  that  the  pressure  gradually  rises  to 
4.7  atmospheres.  This  pressure  is  kept  up  (while  the  di- 
gester is  rotating  about  4  times  per  hour)  until  samples 
show  that  the  raw  material  is  transformed  into  a  pulp, 
which  as  a  rule  requires  about  8  to  9  hours  time.  After 
boiling  is  finished,  the  contents  are  discharged  into  a  cis- 
tern of  draining  stones  or  perforated  wooden  walls  ar- 
ranged below  the  digester,  and  later  on  washed  and  disin- 
tegrated. The  presence  of  the  acid  phosphate  of  lime  (see 
leach  making)  is  considered  to  prevent  the  stuff  from  be- 
coming reddish  in  boiling. 

A  new  American  patent  of  Flodquist  is  described  and 
illustrated, under  No.  525,540. 

While  until  now  sulphite  stuff  digesters  were  heated 
either  from  inside  by  direct  steam  or  from  outside  by 
means  of  a  steam  jacket,  whereby  the  former  method 
caused  a  disadvantageous  and  uneven  dilution  of  the  leach 
and  the  latter  on  account  of  the  high  steam  pressure  re- 
quired, made  necessary  a  very  strong  and  expensive  jacket, 
according  to  the  present  invention  the  digester  is  heated 
from  outside  by  means  of  hot  air  or  hot  gases,  e.  g.,  com- 
bustion gases  free  from  smoke  of  about  300 °C.  Because 
air  does  not  need  to  be  under  pressure  to  be  heated  to  the 
required  temperature,  the  mantel  can  be  made  of  quite 
thin  sheets.  Because  the  mantel  does  also  not  need  to 
be  especially  tight,  it  can  be  composed  of  single  pieces, 
which  can  easily  be  taken  off,  to  lay  free  the  digester. 

The  boiler  A  is  resting  with  hollow  pins,  BB,  in  boxes 
C,  and  is  by  means  of  the  worm-wheel  D  and  the  worm 
Dl  made  to  rotate.  A  pipe  L  serves  to  test  the  inner  steam 
pressure.  As  usual,  a  manhole,  N,  is  provided.  The  jacket, 
to  prevent  radiation  of  heat,  is  hollow  and  filled  with  as- 
bestos or  mineral  wood.  The  cylindrical  body,  E,  of  the 
jacket  is  connected  with  the  walls  of  the  digester  by  the 
angle-iron  01  and  revolves  like  the  right  head-wall  El  to- 
gether with  the  digester.  Whereas  the  left  head-wall,  E2, 
which  carries  the  inlet  H  for  the  hot  air  or  the  hot  gases, 
does  notyrevolve.  With  the  ring,  e,  it  turns  on  the  hol- 
low shaft,  B,  and  at  Y  it  is  supported  against  the  middle 
revolving  part  of  the  jacket.  In  the  right  head- wall  are 
arranged  in  a  circle  a  number  of  holes,  0,  leading  to  a  fixed 
hollow  space,  Nl.  The  hot  air  enters  at  the  left  through 


THE    MANUFACTURE    OF    CELLULOSE. 


125 


the  pipe  H  into  the  space  between  jacket  and  digester,  sur- 
rounds the  latter  and  reaches  through  the  openings,  0,  in 


Fig.  56. 

the  right-hand  head  wall  the  hollow  space  Nl,  from  which 
it  is  carried  off  by  pipe  HI. 


126  THE    MANUFACTURE    OF    CELLULOSE. 

In  concluding  this  chapter  a  few  propositions  are  yet  to 
be  mentioned  in  regard  to  construction  and  lining  of  sul- 
phite digesters. 

A  Mr.  Wagg  in  America,  like  Mitscherlich,  lines  the  di- 
gester with  thin  sheets  of  lead,  lays  upon  this  asbestos  pa- 
per and  upon  this  8  inches  thick  of  bricks  of  one  foot 
square.  Every  brick  is  then  severed  to  the  digester  wall  by 
a  bolt  in  such  manner  that  the  head  is  let  into  the  brick 
and  the  nut  is  put  on  outside.  The  bricks  have  furrows 
all  around,  which  by  means  of  blunt  tools  are  filled  with 
lead,  swallow-tail-like  and  made  tight  with  it.  The  heads 
of  the  bolts  are  also  covered  with  lead  and  the  bolts  them- 
selves are  flattened  on  one  side,  so  that  the  acid  alongside 
of  them  through  a  Gut-out  in  the  nut  can  go  outside, 
when  the  lining  is  leaking.  It  is  thus,  as  in  Frank's  di- 
gester, made  possible  to  find  out  where  a  leak  occurred  in- 
side and  easily  repair  it. 

In  the  sulphite  digesters  of  Frambach  and  Dart  in  Kan- 
kauna  and  Vollrath  in  Shebaygan,  Wisconsin  (American 
patent  No.  348,159),  where  until  now  the  sulphite  stuff 
digesters  were  provided  inside  with  a  lead  lining,  accord- 
ing to  the  present  invention  an  acid  proof  and  elastic  coat- 
ing with  enamel  is  employed. 

The  digester  illustrated  in  fig.  57  consists  of  single 
tubular  sections  provided  with  flanges  and  the  head  and 
bottom  piece  B;  the  different  parts  are  with  their  flanges 
connected  by  screw-bolts.  For  the  purpose  of  tightening 
rings  of  lead,  D,  are  laid  between  the  flanges.  All  parts 
mentioned  are  covered  with  enamel  on  the  inside  up  to 
part  of  the  flanges.  The  digester  is  heated  by  a  bent  steam 
pipe,  E,  which  is  provided  outside  with  a  coat  of  enamel. 
For  the  air-tight  connection  of  it  to  the  bottom-plate  ,B, 
the  lead-rings,  I,  are  provided. 

To  coat  the  different  parts  of  the  digester  with  enamel 
they  are  first  treated  with  acid,  then  scrubbed  with  sand, 
rinsed  off,  dipped  into  hot  lime  water  and  dried.  The  parts 
are  then  wiped  off  with  a  sponge  and  the  first  coat  of 
enamel  is  put  on.  After  this  has  dried,  the  pieces  are 
heated  in  a  muffel  until  the  melting  of  the  enamel.  After 
cooling  off,  the  second  coat  is  put  on  and  also  dried  and 
melted.  In  enameling,  any  vitreous  enamel  which  is  acid- 
proof  and  elastic  can  be  used.  A  suitable  mixture  for  the 
first  coat  consists  of  5  parts  of  lime,  10  parts  of  feldspar, 


THE    MANUFACTURE    OP    CELLULOSE. 


127 


5  parts  of  carbonate  of  soda,  50  parts  of  white  sand,  50 
parts  of  lead  oxide  and  20  parts  of  boracic  acid,  which  are 
mixed  and  fluxed  together,  then  ground  and  stirred  with 
water  to  a  thin  mass.  For  the  second  coat  the  above  men- 
tioned substances  can  be  employed,  adding  10  parts  of 
bone-ash,  5  parts  of  talcum  and  4  parts  of  cryolite,  which 
are  mixed  and  fluxed  together  with  great  heat  to  a  liquid 
glass,  poured  into  water  (for  granulations)  ground  very 
fine  and  stirred  up  in  water. 


Fig.  57. 

Lining  for  the  sulphite  digester  of  Goldburg  Harden- 
Poud  in  Rutland,  Vt.,  (American  patent  351,067)  in  place 
of  the  lead  lining  used  hitherto  according  to  the  present  in- 
vention, for  boilers  and  other  apparatuses,  coming  in  con- 
tact with  acid,  a  bronze  is  used  composed  of  100  parts  of 
copper,  33J  parts  of  lead,  10  parts  of  tin  and  4  parts  of 
antimony.  This  bronze  is  claimed  to  be  very  durable  and 
entirely  resistant  against  the  acids  employed  in  producing 
cellulose. 


128  THE    MANUFACTURE    OF1    CELLULOSE. 

A  greater  novelty  than  the  methods  hitherto  mentioned 
is  the  employment  of  an  acid-proof  protecting  mass,  which 
is  offered  by  Wilhelm  Wenzel,  Vienna,  and  which  is  claim- 
ed to  have  proved  practical.  According  to  this  method 
the  protecting  mass  is  put  on  in  liquid  form  with  a  pat- 
tern of  boards,  and  according  to  size  and  form  of  the  di- 
gester, about  60  to  100  millimeters  thick.  In  Mitscherlich 
boilers  of  4  meters  diameter  the  thickness  amounts  to  125 
millimeters.  At  the  bottom  the  coat  must  be  heavier  and 
rounded  towards  the  cylinder.  Revolving  digesters  of  2J 
to  3  meters  diameter  require  a  coat  of  80-100  millimeters, 
while  for  those  of  2  to  2%  meters  diameter,  70  to  80  milli- 
meters thickness  are  sufficient.  The  work  requires  3  to  4 
weeks.  When  completed  the  lining  of  the  digester  is  ex- 
posed for  several  hours  under  pressure  to  a  temperature  of 
140  to  150 °C.  This  causes  -cracks,  which  are  cut  open  and 
again  covered  with  the  mass.  This  is  repeated,  until  no 
more  bad  places  show  up  and  for  finish  a  coat  of  4  to  5 
millimeters  thickness  of  very  fine  mass  is  applied.  Accord- 
ing to  experience  this  last  coating  is  used  up  in  2  to  3 
months,  but  can  be  easily  replaced  with  a  brush  in  one 
hour  by  two  men,  and  after  two  more  hours  the  digester 
can  be  used  again  for  boiling.  The  4  to  5  millimeters  of 
used-up  coating  certainly  goes  into  the  stuff,  but  does 
not  do  any  harm,  it  is  claimed.  As  the  principal  ad- 
vantage is  pointed  out,  that  the  boiler  always  remains  tight 
and  the  sulphurous  acid  can  never  get  near  the  boiler  shell. 
The  coat  of  this  method  amount  to  70  marks  per  square- 
meter  surface  to  be  lined,  where  to  have  yet  to  be  added 
freight,  wages,  etc.  This  method  is  therefore  not  cheap, 
but  if  given  absolute  protection,  it  would  be  a  welcome 
substitute  for  most  of  the  methods  hitherto  employed. 

Later  on  Mr.  Wenzel  has  made  several  changes  in  the 
manner  of  lining  digesters.  He  does  not  employ  leaden 
braces,  but  such  of  phosphor-bronze,  because  such  do  close- 
ly bind  with  the  mass.  The  safety  screws  of  the  lead-lined 
boilers  are  done  away  with  and  are  substituted  by  just  as 
many  small  open  control  holes,  which  permit  the  lining 
to  be  seen  from  outside.  The  application  of  the  mass  is 
done  slowly  and  layer  by  layer,  and  strong  iron  wire  is  laid 
in  crosswise,  so  that  these,  similar  to  the  Monier  method 
in  building,  form  an  iron  skeleton,  giving  to  the  whole 
mass  much  strength  in  holding  together.  The  whole  layer 


THE    MANUFACTURE    OP    CELLULOSE.  129 

is  finally  about  10  centimeters  thick,  and  lastly  porcelaine 
tiles  are  laid  in,  then  slowly  heated  and  the  furrows  occur- 
ing  are  always  coated  again  with  cement,  until  the  lining 
does  not  change  any  longer.  Later  occuring  tears  and 
faults  are  repaired  in  the  same  manner.  The  composition 
of  the  mass  is  secret,  but  it  may  be  said  that  cement  and 
water-glass  form  important  constituents  of  it.  A  special 
value  of  the  described  lining  is  in  the  saving  of  fuel.  The 
quantitive  determinations  of  the  heat  used  shows  that 
the  lining  forms  an  excellent  protector  of  heat;  the  radi- 
ating heat  is  thus  reduced  to  a  minimum.  The  deter- 
minations resulted  a  saving  of  25$  of  heat  as  against  a 
digester  lined  with  lead. 

A  revolution  in  the  making  of  digester  linings  seems 
to  be  caused  by  the  invention  of  Herr  Director  Brungger 
in  Cunnersdorf,  as  thereby  a  rapid,  entirely  safe  and  very 
cheap  method  is  given,  which  has  already  proved  to  be 
practical  in  many  years  use  in  several  factories.  The  es- 
sence of  the  patented  invention  consists  in  producting  a 
thin,  impenetrable  crust  at  the  inner  digester  wall  by 
introducing  a  sulphite  leach,  a  sulphate  of  lime  solution 
into  the  boiler,  previously  heated  from  outside  and  charged 
with  wood.  This  crust  prevents  every  contact  of  the  metal 
boiler  wall  with  the  sulphurous  acid  and  used  in  boiling  and 
thus  protects  the  digester  against  the  destructive  influence 
of  the  sulphurous  acid. 

With  the  protecting  means  used  until  now,  the  lead 
lining  and  the  many  methods  of  lining  with  bricks  could 
be  provided  only  at  the  expense  of  time  and  money,  the 
formation  of  the  protecting  crust  costs  neither  time  nor 
money.  When  the  protecting  crust  is  once  formed  it  never 
requires  repairing  and  even  a  renovation  of  it  seldom  be- 
comes necessary. 

In  employing  linings  of  lead  and  bricks  of  any  kind  the 
digesters  are  withdrawn  from  uso  during  making  and  re- 
pairing of  the  protecting  lining. 

In  the  digesters  at  Cunnersdorf,  near  Hirschberg,  for 
instance,  while  they  had  the  lead  lining,  about  210  opera- 
tions were  made  per  year  (the  balance  of  the  year  was  used 
in  repairing  the  lead  lining,)  against  almost  300  opera- 
tions, after  they  were  provided  with  the  protecting  crust. 
In  the  figures  the  renovation  of  the  lead  lining  is  not 
taken  into  consideration.  The  producing  capacity  of  a  di- 


130  THE    MANUFACTURE    OF    CELLULOSE. 

gester  with  protecting  crust  is  according  to  this  almost 
one-half  larger  than  if  provided  with  a  lead  lining. 

The  inventors  mark  another  advantage,  the  cessation  of 
the  damaging  to  the  boiler,  connected  with  the  leaking 
of  the  linings  of  lead  or  bricks,  as  well  as  the  rapid  using 
up  caused  by  this,  and  the  possibility  of  an  explosion.  The 
crust  is  entirely  impenetrable,  adheres  firmly  to  the  di- 
gester, but  can  be  taken  off  in  a  few  hours  and  just  as 
quickly  renewed.  The  inventors  have  after  about  one  year's 
work  of  the  boiler  removed  the  crust  and  at  the  inspection 
of  the  inner  digester  wall  by  the  officials  of  the  society  for 
boiler  revision  it  was  found  that  no  corrosions  whatever 
could  be  discovered  in  the  digester  walls.  After  working 
four  months  longer  it  has  been  settled  by  other  eminent 
experts  in  the  same  way,  that  the  iron  mantel  was  without 
fault  and  the  iron  appeared  as  if  it  had  come  directly  from 
the  rolling  mill.  The  digester  provided  with  the  protect- 
ing crust  therefore  offers  greater  security  in  working, 
which  is  increased  by  the  fact  that  it  works  with  very  lit- 
tle over  pressure.  The  digesters  also  work  with  much  less 
consumption  of  steam,  because  in  consequence  of  the  inter- 
mittent work  they  never  get  cold. 

Against  other  linings  the  crust  produced  by  sulphite 
leach  offers  the  advantage  that  during  boiling  it  completes 
and  renews  itself,  if  cracks  or  holes  should  occur,  that 
consequently  it  always  remains  fresh  and  complete.  The 
heating  from  outside  by  steam  jacket  also  permits  easy 
regulation  of  temperatures  and  prevents  increasing  dilu- 
tion of  the  leach,  produced  by  the  introduction  of  direct 
steam. 

To  the  above  mentioned  experts  also  belongs  Professor 
Reuleaux,  who  settled  that  with  the  protecting  crust  as  a 
rule  2  to  3  millimeters  thickness  is  really  a  protection  for 
the  digester  itself,  because  his  testimony  says  that  the 
iron  surface,  becoming  free  under  the  layer,  has  proved 
to  be  entirely  free  from  rust  and  pores.  Nowhere  in  the 
whole  inside  wall  not  a  spot  eaten  by  the  acid  could  be 
discovered. 

In  America  the  method  has  already  been  introduced.  Not 
only  rotating  digesters,  but  every  horizontal  or  upright  di- 
gester as  well  may  be  provided  with  the  protecting  crust, 
if  but  a  heating  jacket  around  the  digester  is  provided,  as 
the  crust  inside  can  only  be  produced  by  heating  from  out- 


THE    MANUFACTURE    OP    CELLULOSE.  131 

side.  The  stuff  produced  in  such  digesters  is  claimed  to  be 
better  and  stronger,  because  the  sulphite  leach  in  them  re- 
tains its  original  strength  and  is  not  diluted  by  condensed 
steam.  This  has  value  only  in  regard  to  boilers,  in  which 
formerly  boiling  had  been  done  by  direct  steam. 

For  Brungger's  method  not  only  solution  of  bisulphite 
of  lime,,  as  prepared  in  the  production  of  cellstuff  from 
wood  according  to  the  sulphite  process,  are  suitable,  but 
also  solutions  of  sulphate  of  lime,  sulphite  of  lime,  sulphite 
of  strontium  and  diverse  others.  When  using  a  solution 
of  bisulphite  of  lime,  sulphite  of  lime  is  next  separated 
from  the  hot  digester  wall,  which  by  further  action  of 
the  heat  is  decomposed  into  sulphate  of  lime  and  sulphite 
of  lime,  under  liberation  of  water,  sulphurous  acid  and 
sulphur.  When  a  solution  of  sulphate  of  lime  is  used, 
it  is  advisable,  to  prepare  it  by  neutralization  of  a  weak 
sulphuric  acid  solution  with  carbonate  of  lime.  The  de- 
gree of  concentration  of  the  solution  is  of  no  consequence 
for  the  success  of  the  method,  neither  does  it  matter 
whether  the  digester  wall  is  heated  before  or  after  charg- 
ing the  solution.  WThen  producing  cellstuff  according  to 
the  sulphite-process  it  is  advisable,  when  working  with 
dilute  solutions,  to  charge  it  together  with  the  wood 
intp  the  cold  digester  and  then  to  heat  it.  With  concen- 
trated solutions  this  can  not  be  done,  as  the  solution  will 
attack  the  digester  wall  too  much,  before  the  protecting 
crust  has  formed.  In  this  case  the  empty  digester  is  first 
heated  from  outside,  the  solution  then  let  in  and  the  digest- 
er set  in  rotation,  until  the  crust  has  sufficient  thickness. 
The  wood  is  charged  thereafter.  If  a  revolving  digester  is 
used  it  does  not  need  to  be  entirely  filled;  a  fixed  digester, 
however,  must  be  completely  filled  with  the  solution  and  be- 
sides, next  to  the  digester  a  vessel  should  be  placed,  into 
which  part  of  the  solution  can  flow  over,  when  the  solution 
expands  in  consequence  of  the  heating.  The  heating  of  the 
digester  can  either  be  done  by  means  of  a  steam  jacket  or 
the  boiler  may  be  placed  in  a  chamber  of  brick,  through 
which  are  conducted  the  gases  from  a  fire. 

A  method  for  producing  a  lining  for  cell-stuff  digesters 
was  patented  by  Guido  Baerwaldt  in  Germany  under  No. 
70,477.  This  digester  on  its  inside  is  freed  of  oxide  and 
other  impurities  by  boiling  with  acid  and  scrubbing  and 
then  coated  with  a  layer  of  cement,  diluted  with  water,. 


132  THE    MANUFACTURE    OF    CELLULOSE. 

potash  or  soda  lye,  waterglasa,  or  lime  milk,  to  the  thick- 
ness of  some  centimeters.  The  cement  used  may  be  either 
entirely  pure,  or  mixed  with  clean  quarz  sand,  powdered 
glass,  ground  charm otte  or  similar  substance.  Before  the 
ground  layer  of  cement  has  settled,  it  is  well  ground  up 
with  a  pasty  mixture  of  oxide  of  lead  and  glycerine,  this 
last  layer  being  permitted  to  cover  the  cement  layer  to  a 
certain  thickness. 

The  lining  thus  prepared  hardens  after  standing  for  a 
while  and  forms  a  vitreous,  very  hard  and  resisting  crust, 
which  prevents  the  penetration  of  the  sulphite  solution  and 
thus  makes  the  digester  very  capable  of  resisting  and  very 
•durable, 

The  mixture  of  lead-oxide  and  glycerine  can  also  be  ap- 
plied directly  to  the  clean  metallic  digester  wall,  but  the 
Application  is  then  some  more  difficult  than  upon  a  pre- 
vious ground  layer  of  cement.  The  mixture  described  can 
also  be  employed  as  binder  or  as  mortar  when  lining  the 
inner  boiler  wall  with  acid  proof  bricks  or  tiles. 

According  to  the  letters  of  the  American  patent  No-. 
.514,197  of  E.  Meurer  of  Palmer  Falls,  K  Y.,  the  metal  of 
the  sulphite  digester  can  be  completely  protected  against 
the  action  of  the  leach  by  a  coating  of  red  oxide  and 
glycerine.  The  inventor  recommends  100  parts  of  thor- 
oughly dry  oxide  of  lead  ground  up  with  12  parts  of  pure 
glycerine  and  that  the  coat  be  made  about  one-third  cen- 
timeters thick.  The  mass  must  be  used  up  quickly,  be- 
cause it  soon  hardens  into  a  stone-hard  and  well-adhering 
cement.  By  adding  more  glycerine  the  mass  becomes  more 
plastic,  but  dries  slower.  When  desired  to  further  protect 
the  coat  by  a  lining  of  bricks  inside  of  the  digester,  the 
same  mixture  can  be  used  as  mortar  and  it  becomes  almost 
as  hard  as  the  stones  themselves. 

The  same  inventor  describes  in  a  second  patent  a  method 
of  lining  the  digesters  with  lead.  The  sheets  of  lead  are 
laid  against  the  inner  wall  of  the  digester  and  the  edges 
are  soldered  together,  so  that  the  whole  lining  forms  a 
single  piece,  closely  adhering  to  the  boiler  wall.  Because 
the  lead  lining  is  not  connected  with  the  digester  wall  by 
rivets  or  cement  it  will  not  be  influenced  by  the  expan- 
sions and  contractions  of  the  boiler  wall  with  changing 
temperatures.  But  it  must  be  protected  by  an  inside  wall 


THE    MANUFACTURE    OP    CEKLULOSE.  123 

of  fireproof  stones  against  falling    in    when    discharging 
the  digester. 

While  lining  with  lead  the  digester  is  practically 
brought  into  a  horizontal  position.  The  sheets  of  lead, 
when  laid  against  the  wall  are  held  fast  by  a  frame  with 
arms  and  pins. 

After  all  sheets  of  lead  are  put  in  and  by  soldering  to- 
gether the  edges  are  united  into  a  whole1,  the  digester  is 
placed  vertical  and  the  brick  lining  is  then  built  up.  As 
the  wall  rises,  the  pins  and  supports  are  gradually  removed 
and  finally  also  the  middle  beam  of  the  frame. 

Another  invention,  to  make  the  digesters  acid-resisting, 
is  by  Henry  W.  Stebbins  in  West  Carrollton,  Ohio  (Ameri- 
can patent  528,339),  is  as  follows. 

The  overlapping  sheets  of  the  boiler  wall,  to  procure  a 
smooth  inside  face,  are  provided  with  a  layer  of  Portland 
cement,  upon  which  the  lead  lining  is  to  lay.  The  lead 
lining  is  fastened  by  lead-rivets,  reaching  through  holes 
in  the  digester  shell  and  in  the  layer  of  cement  and  the  in- 
side is  soldered  together  with  the  lead  sheet.  Upon  the 
lead  lining  goes  a  layer,  consisting  of  a  poor  conductor  of 
heat,  such  as  Portland  cement  with  asbestos,  with  an  ad- 
mixture of  lamp-black,  sulphate  of  barium,  oxide  of  lead 
and  waterglass,  to  make  the  porous  layer  of  cement  and 
asbestos  resistant  to  acid.  A  suitable  proportion  is  given 
in  the  letter  of  patents.  As  10  parts  of  sulphate  of  barium, 
8  parts  of  oxide  of  lead,  2  parts  of  lamp-black  and  a  solu- 
tion of  waterglass  of  12°  Re.  Then  follows,  built  in  with 
cement,  a  layer  of  hard  burned  porous  bricks,  formed  un- 
der hydraulic  pressure.  The  next  layer  consists  of  Port- 
land cement  and  quarz  sand,  lampblack,  sulphate  of  barium, 
oxide  of  lead  and  waterglass  again  mixed  in.  It 
should  have  the  consistency  of  mortar  and  is  poured  be- 
hind the  innermost  layer  of  glazed  tiles. 

In  England  instead  of  cement  for  the  tiles  a  plastic  mass 
made  of  asbestos  and  waterglass  of  1.5  spec.  grav.  is  used, 
serving  to  close  up  the  joints. 

N.  P.  Wedege  of  Drontheim,  had  patented  in  Germany 
under  No.  78,966,  a  discharging  arrangement  on  fixed 
cellulose  digesters  and  says  the  following  about  it: 

Until  now  in  discharging  the  digester  the  acid  was  gen- 
erally first  let  out  by  a  special  pipe  attachment,  then  the 
upper  cover  was  opened  and  the  digester  filled  with  cold 


134  THE    MANUFACTURE    OF    CELLULOSE. 

water  to  wash  the  mass  and  to  cool  off  the  digester  when 
the  mass  was  shoveled  out  by  hand.  By  this  process  the 
digester  ia  exposed  to  sudden  and  repeated  changes  of 
temperature,  which  has  a  damaging  effect  on  material  and 
lining,  and  besides  causes  a  direct  loss  in  heat  and  time, 
when  the  digester  is  to  be  filled  again. 

Often,  also,  the  digesters  were  discharged  by  rinsing 
with  water,  but  in  this  the  changes  of  temperature  have 
also  had  an  injurious  influence,  and  then  a  large  supply 
of  water  was  always  necessary.  Finally  the  blowing  out  of 
the  digester  by  means  of  the  inner  steam  pressure  was 
employed;  but  the  inconveniences  are  perhaps  greater  in 
this  method  than  in  the  former.  During  emptying  a 
vacuum  is  charged  and  the  consequence  often  was  that 
the  inner  linings  were  injured.  Besides  the  undissolved 
knots,  etc.,  were  crushed,  whereby  the  stuff  was  soiled. 

The  hereafter  described  method  aims  to  empty  the  di- 
gester by  its  lower  manhole,  which  by  means  of  a  mechan- 
ism, specially  built  for  the  purpose  and  by  the  steam 
pressure  conveniently  discharges  from  the  digester  stuff 
and  liquid.  The  mixture  is  then  conducted  to  the  stuff- 
basin,  where  it  is  effectively  sprinkled  with  water,  so  that 
the  badly-smelling  leach  is  mixed  with  pure  water  and  runs 
off  through  the  outlet-pipe.  The  peculiarity  of  the  dis- 
charging arrangement  is  that  the  lower  manhole  can  be 
conveniently  opened  by  an  arrangement,  provided  at  the 
upper  manhole. 

In  fig.  58,  a  is  a  plate,  lying  against  the  edge  of  the  neck 
of  the  lower  manhole.  During  boiling  this  plate  is  pressed 
tightly  against  the  cover,  b,  partially  by  the  pressure  pre- 
vailing in  the  digester,  and  partially  by  a  screw  let  through 
the  movable  guard  bl.  The  plate,  a,  is  by  the  rods,  a2, 
also  connected  with  a  sieve,  c,  lying  against  the  inner  lin- 
ing, d.  By  this  means  an  open  space,  e,  is  formed  for 
the  steam,  which  during  boiling  enters  through,  f,  and 
usually  serves  to  heat  the  charge  of  the  boiler.  The  rods, 
a2,  above  the  sieve  form  eyes,  by  which  they  are  connect- 
ed by  joints,  a3,  with  a  larger  ring,  g.  This  ring,  g,  is 
hung  to  a  rod,  h,  which  is  joined  to  a  spindlescrew,  h2; 
the  latter  goes  through  the  upper  manhole.  The  upper 
manhole  cover,  i,  is  provided  with  a  hole  in  the  middle, 
over  which  is  a  collar  or  hull,  j,  upon  which  rests  a  large 
nut,  kl,  by  means  of  which  the  spindle,  k2,  can  be  moved 


THE    MANUFACTURE    OP    CELLULOSE. 


135 


up  and  down.  When  the  digester  is  working  and  there- 
fore the  screw  is  not  used,  this  nut  is  covered  by  a  cap 
and  this  again  is  secured  by  a  smaller  nut,  k2,  screwed 
on  the  shaft,  h.2.  All  parts  inside  of  the  digester  are 


Fig.  58. 

covered  with  lead  for  protection  against  the  action  of 
the  leach  or  are  made  of  an  acid  proof  material.  After 
boiling  is  finished  the  discharging  is  done  in  similar 


136  THE    MANUFACTURE    OF    CELLULOSE. 

manner:  First  the  gas  is  blown  off,  for  instance  through 
the  opening,  ml,  of  the  upper  manhole,  then  the  lower 
guard,  bl,  is  loosened  and  after  removing  the  nut,  b2,  is 
taken  off.  During  this  work  the  plate,  a,  is  held  suf- 
ficiently tight  by  the  pressure  in  the  digester.  In  place 
of  the  guard,  b,  a  piece  of  pipe  is  then  set  in  and  fastened 
by  rest  screws.  This  piece  of  pipe  connects  the  digester 
with  a  stuff  basin  below.  Then  steam  is  admitted  by 
means  of  a  perforated  pipe,  through  the  opening,  m2, 
above  the  plate,  a,  which  goes  through  the  digester  in  sev- 
eral windings,  and  finally  by  turning  of  the  nut,  kl  (laid 
free  by  taking  off  the  cap),  the  whole  lower  locking-ar- 
rangement is  lifted  up  into  the  digester.  The  continuous 
incoming  steam  makes  the  creation  of  a  vacuum  impos- 
sible, and  by  causing  the  whole  charge  to  move,  stuff 
and  acid  flow  through  the  attached  piece  of  pipe  into  the 
stuff-basin. 

The  whole  operation  goes  on  conveniently  and  safely, 
and  the  great  advantage  is  gained  of  keeping  the  digester 
warm,  a.nd  retaining  all  gas  for  the  next  operation.  At 
the  same  time  the  stuff  runs  out  quickly  and  evenly,  with- 
out getting  soiled.  When  all  stuff  is  removed  from  the 
digester,  the  steam  is  shut  off  and  plate,  a,  is1  screwed 
down  again  in  its  place.  To  fill  the  digester  again  with 
wood  the  upper  manhole  must  be  opened.  For  this  pur- 
pose the  nut,  kl,  is  altogether  screwed  off  the  spindle,  h2, 
and  this,  by  means  of  a  chain,  hooked  into  the  upper 
ring,  h3,  is,  together  with  the  shaft,  hi,  let  down  into  the 
vessel,  until  a  wedge  pushed  for  this  purpose  in  the  spin- 
dle, h2,  comes  to>  rest  upon  the  cross  piece,  h5,  arranged 
at  the  upper  manhole.  The  manhole  cover,  i,  is  then  re- 
moved and  the  digester  is  filled.  When  this  is  done,  i  is 
put  on  and  the  shafts,  hi  and  h2,  are  lifted  and  secured. 

In  regard  to  the  armatures  of  the  digester,  the  bushings 
and  valves  are  at  present  mostly  made  of  phosphor  bronze, 
which  offers  the  most  resistance  to  the  acid  leaches.  Other 
resistant  material  may,  however,  be  employed,  as  for  in- 
stance C.  Curtis  and  N".  M.  Jones  in  Massachusetts  and 
Maine  had  an  outlet  pipe  for  sulphite  digesters  patented 
in  America,  which  is  claimed  to  answer  the  same  purpose. 
According  to  their  statements  an  iron  outlet  pipe,  lined 
with  cement  and  protected  at  both  ends  by  rings  of  a 
metal  is  not  attacked  by  the  acid  leach. 


THE    MANUFACTURE    OF    CELLULOSE. 


127 


Fig.  59  shows  the  iron  pipe,  a,  with  the  flanges,  al  and  a2. 
Upon  the  lower  flange  is  screwed  a  ring,  a3,  of  lead  or 
phosphor-bronze,  protecting  inside  and  forming  an  inside 
flange.  Into  this  pipe  is  pushed  one  or  more  pipes,  b, 
pressed  out  of  a  mixture  of  Portland  cement,  quartz  and 
waterglass.  When  several  pipes  are  used,  the  joints  are 
cemented  when  put  in.  The  cement  pipe  has  a  somewhat 
smaller  diameter  than  the  inside  of  the  iron  pipe,  so  that 
between  both  pipes  a  ring-like  hollow  space  is  left.  By 


ezr 


a; 


Fig.  5 


Fig.  60. 


strips,  e,  of  wood  pushed  between  the  cement  pipe  is  given 
a  concentric  position  to  the  outer-pipe,  as  shown  in  fig. 
60,  representing  a  section  through  the  line  4-4  of  fig. 
59.  After  the  cement  pipe  is  built  up  to  the  top  the 
hollow  space  between  both  pipes  is  filled  out  with  cement, 
at  the  same  time  the  strips  of  wood  are  drawn  out  and 
the  upper  end  is  protected  by  an  acid  proof  ring,  a4 
(fig.  59). 

In  conclusion  it  may  be  mentioned  that  the  just  de- 
scribed digesters  of  the  different  methods  are  no  longer  an 


138  THE    MANUFACTURE    OF    CELLULOSE. 

indication  of  the  cellulose  produced  by  a  factory,  because 
Ihe  instructions  of  the  different  inventors  have  been  modi- 
fied to  suit  local  conditions  by  the  manufacture,  or  changed 
for  other  reasons.  So  for  instance  was  the  digester  in  the 
Kitter-Kellner  factories  originally  taken  for  but  30  cubic 
meters  capacity.  Now  in  several  such  factories  digesters 
of  40  and  60  meters  capacity  can  be  seen;  indeed  the  author 
has  seen  in  one  of  them  horizontal  boilers  of  even  100  cubic 
meters  capacity,  externally  not  at  all  differing  from  the 
Mitscherlich  digesters,  but  provided  inside  with  other  lin- 
ings and  having  direct  steam  heating.  The  Mitscherlich  fac- 
tories have  also  adopted  the  new  method  of  dressing  the 
wood,  as  well  as  the  Frank  leach  making  method,  and  also 
employ  the  new  disintegrators. 

C.  PRODUCTION  OF  CELLULOSE  BY  MEANS  OF 
THE  ELECTRIC  CURRENT. 

About  this  new  method  nothing  more  has  been  publish- 
ed than  is  contained  in  the  letters  of  patent,  as  printed 
in  the  Papier  Zeitung.  Whether  this  method  will  ever 
cause  a  practical  revolution  in  the  manufacture  of  cellu- 
I6se,  can  not  yet  be  judged.  For  the  sake  of  completeness, 
this  new  result  of  the  industriousness  of  Herr  Karl  Kellner 
may  be  described  as  follows:  This  method  is  based  on  the 
application  of  the  electric  current  for  the  production  and 
continuous  regeneration  of  substances  during  boiling,  de- 
composing and  the  incrusting  substance  of  the  wood.  The 
wood  is  heated,  while  the  electric  current  is  passing 
through  at  the  same  time,  with  such  liquids  or  solutions 
as  under  the  influence  of  the  latter,  furnish  those  means, 
which  act  decomposingly  on  the  incrusting  substances. 

For  this  the  solution  of  the  chlorides  of  metals  are  suit- 
ed and  especially  that  of  sodium  chloride,  as  the  incrust- 
ing substances  of  wood,  straw,  espartos,  etc.,  are  decom- 
posed by  chlorine,  as  well  as  by  certain  of  its  oxygen-com- 
binations, such  as  subchloric  acid  (hydrogen  hypochorite). 

When  the  vegetable  matter  to  be  decomposed  in  desin- 
tegrated  condition  are  heated  in  closed  vessels  with  solu- 
tions of  sodium  chloride  and  at  the  same  time  an  electric 
current  is  passed  through  the  solution,  chlorine  and  soib- 
chloric  acid  are  produced  at  the  one  side  and  hydrate  of 
soda  at  the  other,  the  elements,  chlorine  and  sodium,  lib- 


THE    MANUFACTURE    OF    CELLULOSE.  129 

erated  at  the  poles  (electrodes),  forming  with  water  sub- 
chloric  acid  and  hydrate  of  soda. 

In  decomposing  the  incrusting  substances  by  chlorine 
and  subchloric  acid,  as  well  as  when  heating  subchloric 
acid  by  itself,  hydrochloric  (muriatic)  acid  is  formed,  which 
in  contact  with  sodiumhydrate  reproduces  sodium  chlor- 
ide so  that  a  circulation  takes  place,  and  the  same  liquid 
runs  through  the  whole  process  unweakened. 

The  process  goes  on  smoothly  at  128° C  and  according 
to  the  statement  of  the  inventor  at  that  temperature  a 
snow-white,  unweakened  fibre  of  silky  gloss  is  obtained 
from  wood. 

In  working  this  method  an  arrangement  is  used  consist- 
ing of  three  vertical  digesters,  connected  on  top  and 
below,  lying  in  one  plane.  Both  electrodes  enter  the  outer 
pipes  below  and  into  side  pipe,  in  which  both  electronega- 
tive iones  (chlorine  and  subchloric  acid)  are  rising  during 
heating,  is  filled  the  vegetable  material.  The  liquids  con- 
taining the  iones  and  its  products  of  decomposition  rising 
during  heating,  and  meet  above,  thereafter  descending 
through  the  middle  pipe.  When  passing  the  electrodes 
decomposition  of  the  chlorides  takes  place  again.  Very 
good  results  can  be  obtained  in  this  arrangement  by 
changing  the  current,  whereby  the  second  side  branch  is 
filled  with  wood,  etc.  The  vegetable  matter  is  then  at- 
ternately  submitted  to  the  treatment  with  alkaline  and 
acid  solutions.  The  soda  lye  formed  thereby  acts  decom- 
posingly  on  the  incrusting  substance  in  such  manner  that 
they  are  quickly  dissolved  when  the  current  changes.  To 
produce,  for  instance,  white  cellulose  for  the  manufacture 
of  paper  from  pine  wood,  the  wood  disintegrated  by  the 
usual  wood  choppers  is  charged  in  to  the  digester  and  the 
latter  closed,  whereupon  chloride  of  sodium  solution  is 
let  in.  In  general  on  8$  solution  suffices  and  about  3J 
hours  at  a  temperature  of  about  126 °C  is  required  (count- 
ing from  the  point  of  the  temperature  reached)  to  produce 
from  pinewood,  white,  firm  cellulose  which  can  be  used 
for  finer  papers. 

The  boiling  itself  is  done  in  vessels,  the  inside  of 
which  is  lined  with  lead  or  other  resisting  substances.  The 
following  well  proven  arrangement  (fig.  61)  consists  of 
both  fixed  digesters  A  and  B,  which  are  connected  below 
by  the  pipes  I,  above  by  the  pipes  H,  and  provided  with 


140  THE    MANUFACTURE    OF    CELLULOSE. 

charging  opening  E  and  below  with  discharging  open- 
ings. Perforated  plates  at  the  upper  and  lower  ends 
prevent  the  fibres1  from  being  carried  along  by  the  cur- 
rent and  clogging  the  pipes.  The  two  pipes  H  make  con- 
nection with  a  smaller  intermediate  vessel  L,  which  carries 
gauge-glass,  macrometer,  safety-and  discharging  valve  and 
a  pipe  T,  which  can  be  shut  off  by  valve  V,  the  prolonga- 
tion of  which  forms  a  coil,  lying  in  a  cooling  tank  P.  The 
vessel  L  ends  in  pipe  K,  which  leads  below  the  bottoms  of 
the  digester  and  then  runs  out  into  fork-like  branchings  I, 
which  turning  up  at  both  sides,  run  into  the  bottoms  of 
the  digesters.  Into  these  pipes  at  M  and  N  the  two  carbon 
electrodes,  R  and  S,  are  introduced  insulated.  After  the 
digesters  are  filled  with  wood  and  a  solution  of  chloride 
of  sodium  is  let  in  until  it  becomes  visible  in  the  gauge- 
glass  of  the  vessel  L,  valve  V  and  all  openings  are  closed, 
into  the  heating  pipes  running  through  the  digesters,  and 
steam,  as  dry  as  possible,  is  admitted. 

Because  the  contents  of  A  and  B  are  expanded  by  the 
heat,  they  rise  through  H  into  L,  thus  causing  a  descend- 
ing current  through  pipe  K.  When  leaving  K  the  liquid 
divides  and  rises  again  in  the  direction  of  the  arrow 
through  pipe  I,  to  enter  again  into  the  digesters  A  and  B, 
and  to  repeat  this  circulation.  In  passing  of  the  liquid  at 
the  electrodes,  when  the  current  is  closed  the  decom- 
position commences  and  the  before  mentioned  side-pro- 
cesses take  place.  When  at  M  the  positive,  at  N  the 
negative  current  is  entering,  the  incrusting  substance  of 
the  wood  contained  in  B  is  submitted  to  energetic  oxida- 
tion on  account  of  the  action  of  the  chlorine  or  its  de- 
rivatives, while  in  A  the  resins  existing  in  the  wood,  con- 
tained in  there,  are  saponified.  The  products  of  decom- 
position (as  far  as  they  are  soluble)  meet  in  the  vessel  L  and 
act  upon  each  other  in  such  manner  that  as  end-product 
chloride  of  sodium  is  formed  again,  the  hydrochloric  acid 
formed  at  the  anode  decomposing  the  organic  compounds 
coming  from  the  cathods  and  separating  the  organic  mat- 
ter, regenerates  the  original  solution  of  chloride  of  lime, 
while  the  separated  organic  matter  by  the  continuously 
renewed  influence  of  the  chlorine  and  its  combinations  is 
decomposed  into  products,  which  either  remain  in  solu- 
tion or  escape  in  the  form  of  gas. 

After  the  process  has  been  conducted  in  the  manner  de- 


THE    MANUFACTURE    OF    CELLULOSE. 


141 


scribed  for  about  one-quarter  to  one-half  hour,  the  cur- 
rent is  changed.  Thereby  by  the  alternating  influence  of 
chlorine  and  soda  upon  the  wood  its  dissolution  is  quick- 
ened. Therefore,  the  changing  of  the  current  is  repeated 
often,  until  the  fibre  is  laid  bare,  which  at  a  temperature 
of  the  leach  of  about  126 °C  is  affected  after  3  to  3J  hours. 
The  inactive  gases  evolved  during  the  operation,  which  ac- 
cumulate in  the  intermediate  vessel  L  are  by  the  occa- 


Fig.  61. 

sional  opening  of  the  valves  V  driven  into  the  cooling 
and  condensing  apparatus. 

When  the  work  is  carried  on  in  the  manner  described 
above,  snow-white  cellulose  is  obtained  from  the  vessel, 
which  at  the  end  of  the  process  had  the  unode  under  it, 
and  this  can  be  used  for  the  finest  sorts  of  paper  without 
bleaching,  while  the  product  from  the  cathode  vessel  is 
colored  somewhat  yellowish  by  the  alkali  formed  at  the 
end  of  the  process,  and  after  washing  needs  to  be  treated 
with  a  very  weak  solution  of  chloride  of  lime. 


142  THE    MANUFACTURE    OF    CELLULOSE. 

Eepeated  experiments  have  proved  that  it  is  of  great- 
er advantage  not  to  treat  the  wood  any  more  in  metal  ves- 
sels, but  in  open  cisterns  of  masonry,  consequently  to  work 
without  pressure.  The  cisterns  consist  of  cement  mason 
work  and  are  lined  with  hurned  clay  tiles.  The  cut  wood 
is  soaked  with  a  salt  solution  before  filling  it  in  the  cistern. 
The  electric  current  produced  by  dynamo  machines  and 
conducted  through  the  mass  evolves  from  the  salt  chlorine 
and  sodium,  which  accumulate  at  the  poles  and  act  partial- 
ly dissolving,  partially  bleaching.  By  pressing  a  button 
the  current  is  from  time  to  time  reversed,  so  that  the 
sodium  goes  to  the  pole,  where  previously  chlorine  had 
accumulated,  and  the  chlorine  to  the  pole,  where  before 
soda  had  appeared.  By  this  changing  treatmnet  with  soda 
and  chlorine  the  wood  suffers  complete  dissolution  and 
bleaching,  and  the  chloride  of  sodium  is  continuously  re- 
generated. 

At  a  most  convenient  site  in  Hallein,  near  Salzburg, 
reputed  for  its  strong  brines,  Herr  Kellner  has  already 
made  a  plant  on  a  large  scale,  according  to  his  latest 
system. 

Now,  after  four  years,  a  conclusive  opinion  cannot  yet 
be  passed  about  Dr.  Kellner's  process  to  produce  cellu- 
lose by  means  of  the  electric  current,  at  least  in  a  perfect, 
practical  shape.  The  inventor  himself  has  authorized  the 
writer  to  make  the  following  statement  about  the  present 
stand:  The  electrolytic  cellulose  manufacturing  method, 
as  such,  on  a  smaller  scale,  works  quite  well,  but  until  now 
it  could  not  be  introduced  into  large  practice,  because  the 
apparatuses  of  the  decomposition  cells  required  so  many  re- 
pairs that  the  advantage  offered  by  the  process  were 
counterbalanced.  Dr.  Kellner  has  for  this  reason  left  the 
process  entirely  for  some  time,  and  set  himself  especially 
to  the  improvement  of  the  electrolytic  parts  of  the  ap- 
paratus; he  has  succeeded  in  this  to  such  a  degree  that  he 
has  accomplished  the  most  difficult  part  of  the  industrial 
electrolysis,  i.  e.,  the  spitting  of  common  salt  into  its 
components,  practically  on  a  large  scale,  so  that  already 
two  large  soda  and  chloride  of  lime  factories  in  England 
are  almost  completely  filled  up  accordingly  and  also  in 
Austria  such  an  establishment  is  going  to  be  built.  These 
experiments  and  labors  made  in  other  directions  have  not 
directlv  benefited  the  electrolytic  cellulose  manufacturing, 


THE    MANUFACTURE    OP    CELLULOSE. 


but  have  removed  these  difficulties,  which  until  now  were 
in  the  way  of  the  industrial  employment  of  the  electro- 
lytic cellulose  process  and  now  soon  after  finishing  the 
plants  designed  for  this  purpose  the  experiences  gained 
will  be  of  value  in  the  manufacture  of  the  electro-cellu- 
lose. The  electric  process  itself,  as  said  before,  is  excellent, 
the  paper  made  of  such  cellulose  is  very  solid  and  pure. 
To  work  the  process,  however,  especially  in  regard  to  the 
choosing  of  materials  was,  until  the  electrochemic  soda 
and  chlorida  of  lime  process  were  worked  out,  too  expen- 
sive. The  question  as  to  the  practical  value  of  the  method 
must  therefore  be  left  open  for  some  time. 

In  connection  with  this  it  may  be  mentioned  that  Herr 
Kellner  had  also  patented  the  electric  bleaching  method 
as  such  and  indeed  "La  Papeteric"  in  France  describes  this 
as  follows: 

"The  process  in  bleaching  vegetable  fibre,  which  is  the 
object  of  this  patent,  is  ba,sed  upon  the  observation  that 
the  coloring  substances  adhering  to  the  fibre  are  by  the 
alternating  application  of  chlorine  and-  alkalies  easier 
transformed  into  water-soluble  combinations,  than  by 
chlorine  alone.  This  occurrence  is  caused  by  the  chlorine,, 
before  transforming  the  coloring  substances  into  water- 
soluble  combinations,  causing  the  formation  of  intermedi- 
ate products,  insoluble  in  water,  but  soluble  in  alkalies. 
When,  therefore,  after  the  intermediate  products  are  trans- 
formed into  an  alkaline  solution,  the  chlorine  is  acting 
again,  not  only  chlorine  must  be  saved,  but  the  bleaching 
must  also  be  affected  in  less  time. 

The  saving  of  chlorine  and  time  will  be  the  more  as  in 
the  ordinary  chlorine  bleach  hydrochloric  acid  (muriatic 
acid)  is  formed,  and  therefore  the  action  of  the  chlorine 
must  be  kept  up,  until  acid-soluble  combinations  take 
the  place  of  the  water-soluble  combinations. 

According  to  the  present  invention  an  alkali-chlorine- 
combination  is  decomposed  by  electrolysis.  Thereby  the 
electronegative  and  the  electro-positive  products  of  de- 
composition (Anion  and  Kathion)  are  alternately  conduct- 
ed through  two  separate  quantities  of  the  bleaching  liquid,, 
then  united  and  again  taken  to  the  electrolytic  apparatus. 

The  arrangement  may,  as  in  fig.  62  and  63,  have  the 
form  of  a  double  bleaching  hollander,  or,  as  in  fig.  64,  that 
of  a  tub  or  of  two  separate  bleaching  hollanders. 


144 


THE    MANUFACTURE    OP    CELLULOSE. 


The  hollander  represented  by  fig.  62  in  plane  and  by 
fig.  63  in  section  is  by  a  wall  aa  through  the  length  divided 
in  three  compartments.  The  fibre  stuff  to  be  bleached  is 
by  pump  d  carried  to  the  middle  space.  It  flows  along  the 
sieve-like  perforated  bottom  and  at  the  end  of  it  gets  under 
the  paddle-wheel  f,  which  is  in  continuous  motion.  By 
this  it  is  taken  up  and  driven  to  the  side  compartments 
cc.  In  one  of  these  compartments  the  electro-positive  de- 
composing solution  is  through  the  perforated  pipe  g  ad- 
mitted to  the  mass  to  be  bleached,  while  in  the  other  com- 
partment the  electro-negative  works  through  a  similar 
pipe  g.  The  bleach-stuff  flows  upon  inclined  bottoms 


Figs.  62-63. 

through  the  side  compartments  to  their  lowest  place  lay- 
ing near  the  original  inlet  and  there  runs  through  the 
openings  cc  into  a  reservoir,  from  where  it  is  again  carried 
to  the  middle  space  by  the  pump. 

Meanwhile  the  two  iones  have  united  again,  the  regen- 
erated decomposing  liquid  accumulates  under  the  sieve  c, 
and  by  the  pump  i,  and  it  is  returned  to  the  electrolytic 
apparatus  j,  through  the  pipe  r.  There,  before  it  reaches 
the  electrodes,  of  platinum  ,carbon  or  zinc,  it  flows  through 
a  sieve  J2. 

The  jointed  anodes  and  cathodes  are  at  its  upper  parts 


THE    MANUFACTURE    OP    CE.KLULQSE. 


145 


separated  by  short  divisions  j3  and  the  so  formed  com- 
partments open  below,  are  alternately  connected  with  the 
one  or  the  other  of  the  pipes  gl  gl,  which  are  arranged 
along  both  sides  of  the  compartment  j.  In  consequence 
of  this  arrangement,  the  one  pipe  conducts  electro-positive, 
the  other  electro-negative  decomposing  liquid  into  the  con- 
necting pipes  gg. 

When  the  electric  apparatus  is  to  be  connected  with 
two  separate  bleach  Hollanders,  the  bleach  mass  in  both 
of  them  is  kept  in  continuous  motion  by  suitably  arranged 
pipes,  and  wash  drums  return  the  decomposing  liquid  to 
the  apparatus.  In  this  case  the  direction  of  the  electric 
current  must  from  time  to  time  be  changed  so  that  the 


fibres   to  be  bleached   are   alternately   submitted   to   the 
action  of  chlorine  and  alkali. 

This  changing  of  the  direction  of  the  current  is  also 
requisite,  when  the  apparatus  is  built  as  in  fig.  64.  The 
bleaching  process  here  takes  place  in  two  cylindrical  tubs 
with  threefold  partitions  in  each.  The  mass  of  fibre  to  be 
bleached  is  introduced  in  the  innermost  space  A  of  the 
tub  and  there  kept  in  continuous  ascending  motion  by 
means  of  a  propeller  screw  p,  set  into  the  bottom.  The 


146  THE    MANUFACTURE    OF    CELLULOSE. 

stuff  flows  over  the  walls  m  into  the  hollow  space  between 
m  and  n  and,  following  the  current  caused  by  the  screw, 
enters  again  into  the  inner  space  through  the  trapeze- 
shaped  openings  ml  in  the  bottom. 

The  circulation  of  the  bleach  mass  could  also  take  place 
in  reversed  direction.  It  would  then  be  driven  out  by 
the  openings  m,  rise  up  between  m  and  n  and  return  over 
the  edge  of  m. 

The  electro-positive  decomposing  liquid  (Anion)  enters 
through  the  pipe  f  into  the  hollow  space  H.  The  lower 
face  of  this  hollow  space  is  solid  and  tight,  the  upper 
is  sieve-like,  perforated  and  covered  with  filter  stones,  so 
that  the  anion  filling  the  space  H  can  come  in  contact  with 
the  bleach  stuff. 

The  electric-negative  decomposing  liquid  (cathion) 
enters  into  the  like  bottom  of  the  other  bleach  tub.  Both 
liquids  flow  through  the  bleach  mass  from  below  upwards, 
enter  through  the  sieve-like  upper  part  of  the  walls  nl  into 
the  space  between  n  and  o  and  from  there  flow  through 
the  pipes  g  into  the  reservoir  q.  By  the  uniting  of  both 
liquids,  taking  place  there  the  solution,  having  been  sub- 
mitted to  decomposition,  is  regenerated  and  again  con- 
ducted to  the  electric  decomposition  apparatus.  Both  tubs 
are  provided  with  water  and  air-tight  covers  Ol,  at  which 
openings  O3,  with  blow-off-valves  are  arranged.  These  open- 
ings permit  the  taking  from  time  to  time  of  samples  and 
the  controling  of  the  bleaching  process.  The  pipes  r 
serve  to  admit  steam  and  to  heat  the  mass. 

In  place  of  two  tubs  whole  rows  of  them  can  be  used 
and  connected  with  each  other  by  pipes,  as  it  done  simi- 
larly with  the  diffusion  batteries  in  sugar  factories.  In 
such  manner  continuous  work  is  possible. 

About  an  improvement  of  his  electric  bleaching  method 
Dr.  Kellner  writes  in  the  Papier  Zeitung  set  1894,  page 
2,486,  as  follows: 

As  easy  as  the  decomposition  of  a  solution  of  common 
salt  into  chlorine  and  sodium  by  the  electric  current  takes 
place,  and  notwithstanding  the  numberless  experiments 
made  it  has  not  become  possible  until  recently  to  find  out  a 
method  which  has  prospects  for  practical  success. 

The  older  methods  failed  principally  on  account  of  too- 
rapid  consignation  of  the  complicated  apparatuses  and  of 
the  insufficient  transformation  of  the  required  motoric- 


THE    MANUFACTURE    OP    CELLULOSE. 


147 


power  into  electro-chemical  work.  Siemens  &  Halske  in 
Vienna  have  now  come  forth  with  methods  different  from 
those  of  Dr.  Karl  Kellner,  which  for  simplicity  leave 
nothing  to  be  desired.  The  following  illustrations  repre- 
sent the  Kellner  method  for  bleaching  of  paper  stuff. 

Fig.  65  shows  the  so-called  bleach-block.  It  consists 
of  the  plates  A,  Al,  A2,  at  one  side  covered  with  platinum, 
which  by  the  rods,  B,  Bl,  B2,  are  united  into  one  solid  body. 
When  such  block  is  set  in  a  hollander  and  connected  with 


A 


JT 


Fig.  65. 

the  clamps  of  a  dynamo  machine,  the  stuff  in  the  holland- 
er is  at  once  bleaching,  after  adding  solution  of  salt.  The 
stuff  is  continuously  passing  between  the  plates,  A,  Al,  the 
electrodes  and  can  therefore  be  bleached  with  little  power, 
as  the  chlorine  evolved  from  the  salt  is  acting  in  status 
nascendi,  the  much  more  powerful  state  of  creation,  as 
well-known.  Fig.  65  shows  a  hollander  with  two  of  the 
blocks  described.  The  salt  solution  is  continuously  used 
over  again,  and  by  adding  fresh  salt,  kept  at  the  original 


148  THE    MANUFACTURE    OF    CELLULOSE. 

strength.  By  the  decomposition  of  20  kilogrammes  of 
salt,  100  kilogrammes  of  stun6  are  claimed  to  be  bleached; 
what  kind  of  stuff  is  meant  is  not  stated. 

When  several  bleach-hollanders  are  placed  in  one  room, 
the  method  represented  in  fig.  66.  is  recommended,  in 
which  for  cheapness  no  platinum  is  used.  Fig.  66  shows 
the  electrolytic  apparatus  in  section  and  plane,  the  elec- 
trodes consist  of  carbon;  they  are  claimed  to  be  cheaper 
and  more  durable.  The  salt  solution  flowing  into  the  ap- 
paratus through  the  pipe,  visible  to  the  left  above  and  pro- 
vided with  a  valve,  must  find  its  way  to  B,  as  indicated 
by  the  arrows,  between  the  electrodes,  arranged  alternately, 
forming  a^number  of  cells.  As  visible  in  fig.  66,  the  hypo- 
chlorite-solution  produced  in  the  apparatus  mentioned 
from  the  salt  solution  flows  at  B  through  the  filter  F  below, 
of  glass  wool  into  the  bleach  hollander.  If  instead  of 
carbon,  platinated  plates  are  employed,  the  filter  can  be 
dispensed  with.  The  drain-box  K  serves  to  receive  the 
bleached  stuff;  the  off-running  salt  solution  is  accumulat- 
ing in  L  and  after  closing  the  valves  h  and  h3  and  opening 
hi  and  h2,  is  by  the  pump  P  used  for  rapid  filling  of  the 
hollander  when  charging  fresh  material.  The  valves  hi 
and  h2  are  then  closed,  h  and  h3  opened  and  by  the  pump 
a  steady  circulation  of  the  salt  solution  through  the  elec- 
trolyser  filter  and  hollander  is  affected  during  bleaching.  A 
further  improvement  of  the  Kellner  bleaching  method  is 
spoken  of  in  the  Centralbladt  fur  Oesterr  Ungar  Papier 
Industrie,  from  which  is  taken  the  following: 

In  the  decomposition  of  common  salt  by  the  electric 
current,  without  using  a  diaphragm,  the  products  of  de- 
composition, chlorine  and  caustic  soda,  unite  in  to  sub- 
chlorite  of  soda,  which  forms  the  effective  constituent  of 
the  bleaching  liquid.  Besides  this  principal  process  several 
side-reactions  take  place  which  lessen  the  practical  effect 
and  mainly  consist  in  the  formation  of  chlorate  and  the  re- 
duction of  already  formed  sub-chlorite  of  soda  to  chloride 
of  sodium.  These  side-reactions  formed  one  of  the  princi- 
pal difficulties  in  working  out  the  electric  bleach  method. 
Then  also  contact  difficulties  and  disagreeable  experiences 
with  the  different  electrodes  came  up.  Carbon  electrodes 
are  certainly  cheap,  but  are  quickly  consumed  and  require 
filtration  of  the  bleach  liquid.  Whereas  platinum  elec- 
trodes, if  anyway  durable,  are  very  expensive  and  on  ac- 


THE    MANUFACTURE    OF    CELLULOSE. 


149 


count  of  the  high  amortisation  add  much  to  the  manufac- 
turing expenses. 

By  introduction  of  his  pointed  electrodes  Dr.  Karl 
Kellner  believes  he  has  found  a  practical  solution  of  the 
question.  These  electrodes  are  plates  of  hard  rubber,  or 
other  resistant  material,  which  in  the  form  of  a  brush  are 
provided  with  platinum  points  and  in  a  box  of  ebonite  are 
connected  for  tension.  With  this  arrangement,  it  is  claim- 
ed, to  produce  under  very  favorable  circumstances  solu- 
tions with  to  1$  active  chlorine,  which  concentration  is 


Fig.  66. 

% 

for  most  requirements  perfectly  sufficient.  The  com- 
position of  the  produced  1$  bleach  liquid  is  with  equal 
conditions  of  current  mainly  depending  on  the  concentra- 
tion of  the  salt  solution  employed  and  on  the  temperature 
observed  in  the  electrolysis. 

The  bleach  liquid,  of  1$  active  chlorine,  produced  under 
normal  conditions  from  10$  salt  solution,  contains: 

2.09$  hypochlorite  of  soda 

0.60$  chlorate  of  soda 

7.90$  undecomposed  chloride  of  soda 

The  6$  chlorine  contained  in  a  10$  salt  solution  conse- 
quently divide  as  follows: 


150  THE    MANUFACTURE    OP    CELLULOSE. 

1.00  Cl  as  Na  Cl  0 

0.2$  Cl  as  Na  Cl  03 

4,7$  Cl  as  Na  CL 

The  bleach  liquid  running  off  is  entirely  clear  and  open 
and  keeps  unchanged  quite  long.  After  standing  for  days 
the  bleaching  strength  decreases,  as  with  solutions  of  chlor- 
ide of  lime;  the  decreasing  is  different,  according  to  wheth- 
er the  liquid  is  kept  in  the  dark  or  in  the  light. 
V.  WASHING,  BLEACHING,  FINISHING  OF  THE 
CELLULOSE. 

These  finishing  manipulations,  although  different  in 
character,  are  not  connected  with  the  kind  of  methods  here- 
tofore treated,  and  may  therefore  be  treated  now,  without 
regard  to  them.  When  the  knots  were  not  bored  out,  or 
sorted  out  before  boiling  the  wood  then  after  the  discharg- 
ing of  the  digesters,  sorting  by  boys  and  girls  must  be  done, 
especially  when  the  wood  had  been  cut  into  slices.  In  this 
case  the  workmen  throw  the  cellulose  on  a  table,  divide 
the  soft  mass  with  the  fingers  and  in  this  manner  easily 
find  the  knots  and  hard  pieces  of  wood,  which  have,  per- 
haps, been  only  partially  boiled.  When  yellowish  and  hard- 
er cellulose  adhere  to  the  knots,  they  are  laid  aside  and 
worked  up  later  on,  to  obtain  an  inferior  cellulose,  so-called 
third  quality.  As,  however,  in  spite  of  all  sorting  the 
knots  do  not  absolutely  disappear  and  a  forcible  dividing 
would  disintegrate  the  fibres  adjacent  to  the  knots,  by 
which  the  quality  of  the  cellulose  would  be  lessened,  it  is 
necessary  to  take  care  that  this  separating  of  the  fibres  is 
done  as  carefully  as  possible.  Mitscherlich  has  employed 
for  this  purpose  a  stamping  mill,  which  however  does  not 
properly  crush  the  stuff,  but  rather  grinds  it,  as  shown  in 
the  following  discription. 

Fig.  67  represents  a  sideview  and  section  of  such  stamp- 
ing mill.  In  about  seven  iron  frames  A  rests  the  thumb- 
shaft  B,  rotating  about  ten  times  per  minute.  The  frames 
are  connected  by  two  pairs  of  heavy  timber,  Cl  C2,  and 
Dl  D2,  which  at  the  same  time  serve  as  guides  for  about  60 
stampers,  one  next  to  the  other,  which  again  reach  to  near 
the  bottom  of  the  stamping-trough  E,  sketched  ;n  &ection, 
which  is  about  15  meters  long,  and  inclining  abor.t  0.6 
meter,  counting  from  the  head  to  the  end.  The  lifting 
thumbs  are  set  around  the  shaft  in  such  manner  that  three 


THE    MANUFACTURE    OF    CELLULOSE. 


151 


or  four  neighboring  stampers  are  not  lifted  at  the  same 
time  with  every  revolution,  but  one  after  the  other;  so  that 
they  work  as  shown  in  fig.  68,  representing  part  of  the  front 
view.  In  this  manner,  the  first  stamper,  at  the  head  of 


Fig.  67. 

the  trough,  when  going  down,  carries  part  of  the  stuff  to 
the  second,  this  one  to  the  third,  and  so  on;  until  finally, 
while  water  is  continuously  running  in,  the  stuff  reaches 
the  other  end  of  the  trough  in  the  form  of  a  thin  pulp. 
As  the  stampers  do  not  quite  reach  the  bottom  and  carry 


152  THE    MANUFACTURE    OF    CELLULOSE. 

below  a  wider  shoe,  but  do  not  touch  at  the  sides  when  the 
one  stamper  falls-  and  the  next  one  is  lifted,  the  stuff  is 
slightly  triturated  in  the  spaces  between  without  injur- 
ing the  fibre  or  crushing  the  hard  pieces  and  knots.  The 
picked  cellulose  is  poured  in  the  lower  end  of  the  stamping 
trough  by  the  workmen,  or,  when  the  sorting  takes  place 
in  an  upper  loft,  in  a  large,  wooden  funnel,  by  which  the 
stuff  is  continuously  fed  to  the  trough.  A  workman  then 
has  to  regulate  this  feeding,  also  the  water  supply  and  at 
times  he  must  assist  the  stuff  to  move  along  the  trough.  By 
more  or  less  closing  the  outlet  opening  of  the  trough,  the 
stuff  is  retained  in  the  trough  for  a  longer  time  and  more 
or  less  worked  through,  as  made  necessary  by  the  quality 
obtained  in  the  boiling  operation.  A  second  necessary  labor 
is  the  washing  of  the  stuff,  that  every  trace  of  leach,  es- 
pecially of  sulphurous  acid  is  removed  from  the  cellulose. 
This,  according  to  Mitscherlich,  is  not  done  in  a  violent 
manner,  but  by  a  system  of  so-called  wash  troughs,  by 
which  though  much  water  is  used  the  fibering  and  wash- 
ing is  done  very  effectively,  and  at  the  same  time  an  assort- 
ing is  effected,  so  that  at  the  end  only  the  finest  fibres  flow 
off,  while  all  heavier  particles  settle  before.  As  it  is  es- 
sential, to  make  the  trough  as  long  as  possible,  in  order  to 
save  space  two  such  troughs  are  generally  arranged  one 
above  the  other.  They  are  given  the  form  shown  in 
fig.  69. 

A  wooden  trough  about  1  meter  wide  and  300  milli- 
meters deep  is  provided  at  the  bottom  with  so-called  sacks 
or  knot-catchers,  in  which  all  knots,  hard  wood  particles 
and  coarse  splinters,  kept  back,  settle;  which  later  on,  when 
cleansing  of  the  troughs  becomes  necessary,  are  let  off  by 
holes  provided  with  bungs.  As  soon  a,s  the  stuff  leaves  the 
stamping  trough,  it  is  next  by  one  or  more  powerful  sprays 
of  cold  water,  not  only  diluted,  but  the  loosely  connecting 
bundles  of  fibres  are  at  the  same  time  washed  apart,  so  that 
the  much  diluted  mass  consists  mainly  of  separate  cellu- 
lose fibres,  floating  side  by  side.  For  more  effective  separa- 
tion the  stuff  is  often  at  the  head  of  the  trough  made  to 
pass  one  or  several  stirrers,  or  a  so-called  knot  beater  is 
used,  as  employed  in  paper  mills,  which  have  centrifugal 
hollanders;  or  the  stuff  is  first  let  over  a  plain,  large  knot 
catch,  formed  of  wooden  slats,  provided  with  a  shaking 


THE    MANUFACTURE    OF    CELLULOSE.  153 


n 


n 


1=1 


L=z 


A 


A 


A 


A 


A 


A 


Fig.  68. 


Fig.  69. 


154  THE    MANUFACTURE    OP    CELLULOSE. 

arrangement.  By  these  arrangements  the  lime,  gyps  and 
coarser  fibres  are  retained,  but  the  small  splinters,  which 
indeed  are  really  but  small  bundles  of  fibres,  not  yet 
separated,  but  otherwise  soft  particles  of  cellulose,  stay  in 
the  stuff,  and  must  be  removed,  as  much  as  possible.  This 
is  done  by  either  one  or  two,  or  a  whole  system  of  plate- 
knot-catchers.  The  whole  stuff  must  go  through  the  nar- 
row slits  of  the  knot-catcher  plates,  which  is  affected  by 
beating  with  an  up  and  down  motion,  which  causes  the 
stuff  to  be  sucked  through.  A  convenient  arrangement  of 
this  kind  is  shown  in  figs.  70  and  71. 

By  an  elevator  or  by  a  worm  the  stuff  is  lifted  from  the 
stamping  trough  and  enters  the  wash-trough  at  A.  It 
flows,  much  diluted  with  water,  through  the  different  sec- 
tions, as  indicated  by  the  arrows,  and  finally  enters  a  small 
trough  B,  from  which  it  runs  on  the  four  plate-knot-catch- 
ers, arranged  side  by  side,  under  it  in  the  trough  C  and 
from  there  it  is  carried  to  the  fillers. 

Lately,  however,  the  Wandel  cellulose  cleaners  are  used. 
They  are  quite  similar  to  the  rotating  knot-catchers  pre- 
viously built  by  the  same  firm.  The  only  practical  al- 
teration is  that  they  are  not  moved  up  and  down  by  pad- 
dle wheels,  but  are  rotated  very  quickly  and  thus  suck  in- 
side the  thin  stuff,  by  which  they  are  almost  totally  sur- 
rounded, and  consequently  they  work  perfectly  noiselessly. 

Lately  Wandel  has  constructed  another  sorting  arrange- 
ment for  cell-stuff  and  patented  it  in  America  under  No. 
478,170.  In  the  Papier  Zeitung  the  description  reads  as 
follows:  The  stuff  to  be  sorted  flows  through  a  trough  a  as 
into  a  tank  al,  in  which  is  set  a  quickly  rotating  sorting 
cylinder  b,  as  its  circumference  provided  with  fine  slits. 
The  fine  stuff  enters  through  the  slits  into  the  cylinder  and 
runs  off  through  the  central  openings  at  both  ends.  Inside 
the  cylinder  are  fastened  the  paddles  d,  forming  with  the 
circumference  an  angle  of  about  45°  and  with  the  rotating 
of  the  cylinder  in  the  direction  of  the  arrow  act  with  suc- 
tion on  the  stuff,  and  acclerate  its  passing.  The  coarse  stuff 
settles  on  the  round  bottom  of  the  trough  and  is  removed 
through  the  channel  h  at  the  side,  the  cover  of  which,  i,  is 
for  this  purpose  opened  without  interrupting  the  work.  For 
totally  discharging  and  cleaning  the  trough  a,  the  opening 
k  is  provided. 


THE    MANUFACTURE    OP    CELLULOSE. 


155 


A  centrifugal  cell-stuff  sorter  is  built  by  Wagner  &  Co. 
and  described  in  the  Papier  Zeitung  as  follows: 

The  cell-stuff,  mixed   with   much   water,   is   conducted 


Fig.  70. 


nr  TJ 


Fig.  71. 

through  the  pipe  d  to  the  lower  narrow  part  of  the  trough 
c,  filling  this  up  to  the  overrun  e,  from  where  it  flows 
over  a  wide  trough,  not  shown  here.  To  get  there,  the 


156  THE    MANUFACTURE    OF    CELLULOSE. 

stuff  must  pass  the  sieve-cap,  consisting  of  the  knot-catch- 
er-plates a.  These  3  mm.  strong  brass  plates  are  provided 
with  straight  slits  of  4-10,  5-10  or  6-10  mm  width.  The 
frame,  in  which  the  plates  are  set,  consists  of  the  foot  piece 
a3  (fig.  73)  of  hardwood,  into  which  are  let  the  vertical 
plates,  also  the  joints  al  and  the  stiffening  bows  of  iron, 
copper  or  bronze  of  60  mm.  width  and  12  to  15  mm. 
height,  which  connect  all  cross-pieces,  and  serve  as  im- 
post for  the  one  meter  long  plates.  There  will  consequent- 
ly be  one  such  bow  for  each  meter  length.  At  the  two 
end-bows  are  fastened  the  bows  a4,  by  which  the  whole 
sieve-cap  can  be  lifted  out,  after  loosening  the  set  screws, 
by  which  the  foot-pieces  a3  are  connected  to  the  walls  g. 
To  take  them  out  is  necessary  as  often  as  the  plates  have 
to  be  thoroughly  cleaned,  and  can  be  made  more  convenient 
by  suspending  the  cap  by  rope  and  pulley.  The  vertical 
plates  are  kept  clean  during  working  by  the  sprinklers  c,. 
of  which  there  are  two  on  each  side  and  which  are  regulated 
by  a  cock  on  each  end.  To  make  the  sieve  cap  tight  at 
both  heads,  the  two  headwalls  i  are  cut  out  in  triangular 
shape  and  set  on  similarly  formed  inside  walls  h  of  the 
tank,  as  shown  by  the  dotted  lines  in  fig.  73.  Where  the 
edges  join,  they  are  lined  with  strips  of  felt  and  the  weight 
of  the  sieve  cap  by  itself  secures  tightness.  A  beater  bl 
which  makes  100  to  120  revolutions  per  minute,  with  its 
wooden  scoops,  going  through  and  resting  on  four  crosses, 
drives  the  stuff  through  the  plates.  The  stuffing  boxes  b, 
of  the  beater  shaft  are  not  fastened  to  the  wooden  tank,  but 
rest  on  the  iron  support  k,  being  thus  independent  of  the 
changes  in  the  wood.  A  box  support  b2  carries  the  end  of 
the  shaft,  besides  the  driving  pulley.  The  heavy  impuri- 
ties settle  in  the  lower  part  of  the  tank  and  can  be  re- 
moved through  the  slide  f .  The  stuff  should  run  down  from 
a  height  of  300  mm.  above  its  level  at  e,  where  it  runs  off 
about  50  to  80  mm.  above  the  upper  plate  a.  The  sprinkle 
pipes  c  are  mainly  for  the  purpose  of  keeping  the  stuff 
in  motion  and  do  not  need  to  work  all  the  time.  The  up- 
per plates  have  by  experience  proved  to  keep  clean  them- 
selves. It  is  claimed  that  it  costs  little  to  work  tl>e  sorter,, 
as  the  cleaning  is  going  on  rapidly  and  the  consumption  of 
power  is  small.  Through  a  sorter  of  2,500  mm.  length 
and  4-10  mm.  slits  4,000  kgr.  of  long  fibred  Mitscherlich 
stuff  will  go  in  24  hours. 


THE    MANUFACTURE    OF    CELLULOSE. 


157 


158 


THE    MANUFACTURE    OF    CELLULOSE. 


The  stuff,  freed  from  splinters  as  much  as  possible  by 
one  or  more  cellulose  cleaners  is  then  run  on  a  filtering  ar- 
rangement, like  a  small  paper  machine,  only  the  sieve  is 
shorter,  made  of  stronger  wire,  meshed  wider  and  does 
not  have  a  shaking  motion.  After  the  so-called  gonch- 


press,  as  a  rule  the  pasteboard  like  stuff  is  passed  through 
a  second  press,  screw  or  lever-press,  in  order  to  obtain  a 
product  as  free  from  water  as  possible.  The  quantity  of 
water  in  cellulose  passed  through  a  second  press  and  then 


THE    MANUFACTURE    OP    CELLULOSE. 


159 


wound  up  in  rolls  as  a  rule  amounts  to  about  50  p.  c., 
sometimes  more. 

Mitscherlich  has  not  himself  used  the  above  described 
filtering  arrangement,  but  the  so-called  hair  cylinder, 
which  turns  out  the  cellulose  in  the  form  of  lumps.  The 


accompanying  illustrations  show  the  same  in  section  and 
plane :  The  cylinder  h,  covered  with  a  sieve  o  f horse-hair,  is 
conical. 

The  stuff  enters  in  the  direction  of  the  arrow,  the  water 
is  thrown  out  by  rapid  rotation  and  the  pasty  stuff  falls 
through  the  opening  a  on  a  felt  f,  which  is  carried  and 


160  THE    MANUFACTURE    OF    CELLULOSE. 

stretched  by  several  rollers  d,  d,  d,;  passes  between  the 
press  rollers  p  p  and  is  carried  away  in  the  direction  of  the 
arrow.  After  this  water  is  pressed  out  from  the  stuff  by 
the  press  rollers,,  the  stuff  b  adhering  to  the  upper  roll  p 
is  scraped  off  by  the  shaver  m,  falling  on  a  table  and  by  a 
hole  in  it  is  directly  filled  into  a  bag,  S,  to  be  shipped  as  so- 
called  lump  cellulose. 

In  late  years  various  apparatuses  have  come  into  use  for 
dividing  the  boiled  wood,  in  place  of  the  stampers,  not 
only  in  the  Mitscherlich  factories,  but  also  in  other  sys- 
tems, among  which  the  so-called  "separator"  has  gained 
the  widest  distribution.  This  does  not  at  all  injure  the 
stuff,  and  with  comparatively  small  power  does  good  work. 
It  is  described  as  follows: 

Fig.  77  and  78  show  it  in  long  and  cross  section.  It 
consists  of  two  wooden  drums  somewhat  conical,  about  5 
meters  long  and  1  in  diameter,  of  which  a  is  the  upper  in 
which  the  stuff  carried  by  an  elevator  enters  at  e.  The 
drums  themselves  are  fixed,  but  inside  of  them  are  mov- 
ing strong  wooden  shafts  c  d,  on  which  are  set  along  a 
spiral  line  a  large  number  of  long  sticks,  which  nearly 
reach  the  circumference  of  the  drum.  The  velocity  of  the 
upper  shaft  c  is  80-100  revolutions  per  minute,  while  the 
lower  makes  about  160  revolutions.  The  thick  stuff, 
which  in  the  upper  drum  is  diluted  with  ibut  little  water 
hy  cock  w,  is  then,  by  the  sticks,  repeatedly  driven  against 
the  circumference,  until  leaving  at  the  other  end  at  f,  it 
falls  into  the  second  drum,  is  there  diluted  with  more  wa- 
ter and  leaves  at  g,  with  fibers  entirely  clear,  and  with  still 
more  water  it  reaches  a  wash  trough,  as  long  as  possible, 
in  which  sand  and  small  knotty  particles  can  settle.  At 
the  end  of  this  wide  trough  one  or  more  wash  drums  are 
arranged,  which  remove  the  surplus  water  and  from  where 
ihe  pulp  runs  either  directly  into  the  bleaching-hollander 
or  is  let  into-  draining  boxes. 

Another  new  system  for  dividing  cell  stuff  is  Engelmay- 
erfs  system  consisting  of  three  patented  apparatuses,  built 
by  the  C.  D.  Bracker  Sons.  The  following  is  said  about  it: 

After  the  wood  is  well  boiled,  i.  e.  dissolved,  it  is  by 
means  of  an  elevator  conducted  to  the  first  apparatus  of 
the  dividing  system,  the  fiberer,  the  task  of  which  is  to 
separate  the  fibres  from  the  boiled  knots  and  the  still 
Tiard  particles  of  wood.  In  the  mixer,  connected  to  this, 


THE    MANUFACTURE    OF    CE-LLUL.OSE.  161 

n n 


162  THE    MANUFACTURE    OF    CELLULOSE. 

the  mixing  and  diluting  is  done.  The  knots  and  particles 
left  hard  are  separated  in  the  sorting  apparatus.  From 
there  the  stuff  is  conducted  through  a  convenient  sand- 
pang,  in  which  are  retained  the  still  present  heavy  par- 
ticles, as  well  as  the  resins,  beaten  off  by  an  apparatus,  ar- 
ranged in  it.  The  succeeding  apparatus,  the  washdrum 
and  filtering  machines,  serve  to  partially  separate  the  wa- 
ter, and  the  stuff  then  reaches  the  "squasher"  in  which 
the  straightening  and  dividing  of  the  fibre  is  effected.  The 
conclusion  of  the  dividing  system  is  formed  by  a  "dis- 
solver,"  from  which  the  stuff  is  conducted  to  the  beating 
engine  and  eventually  to  the  long  sieve  machine.  Knot- 
and-splinter  fangs  are  not  employed. 

In  the  following  the  different  operations  and  apparatus 
are  exactly  described: 

1.  Method  for  dividing  the  cell-stuff  bundles  and 
drawing  out  of  the  fibre:  The  present  invention  forms 
a  method,  to  divide  cell-stuff,  especially  sulphite  cellulose, 
thoroughly  with  preservation  of  the  long  fibre.  This 
could  not  be  achieved  heretofore,  because  the  dividing  of 
the  boiled  cell-stuff  by  mills  and  refiners  was  imperfect 
to  such  a  degree  that  the  stuff  always  contained  indis- 
solved,  connecting  fiber  bundles,  so-called  splinters,  which 
had  to  be  removed  by  special  splinter-fangers.  By  the 
present  dividing  method,  a  stuff  entirely  free  of  splinters 
is  claimed  to  be  obtained,  so  that  the  splinter-fangers  can 
be  dispensed  with. 

The  loosening  of  the  cell-stuff  is  done  in  such  manner 
that  the  boiled  cellulose,  after  it  has  passed  a  draining 
apparatus,  goes  through  two  rollers,  which  revolve  with 
different  velocity  and  of  which  practically  the  slower  re- 
volving roller  has  a  larger  diameter. 

The  rollers  are  so  finely  adjusted  that  only  the  thicker  par- 
ticles, not  quite  boiled  .soft,  are  affected.  These  consist 
of  connecting  fibre-bundles  and  exist  in  the  finished  cel- 
lulose under  the  name  of  splinters,  and  they  are  crushed, 
and  in  consequence  of  the  unequal  velocity  of  the  circum- 
ferences ground  and  dissolved  into  separate  fibres.  The 
single  fibres,  already  produced  in  boiling,  are,  because  the 
rollers  are  adjusted  only  for  the  thick  fibre  bundles,  scarce- 
ly touched  and  cannot,  therefore,  in  passing  the  rollers  be 
torn  by  them.  They  thus  retain  their  original  length. 


THE    MANUFACTURE    OF    CELLULOSE.  163 


Fig.  80 


164  THE    MANUFACTURE    OF    CELLULOSE. 

In  case  the  cellulose  should,  after  passing  the  rollers,, 
still  show  small  splinters,  it  is  made  to  go>  through  a  sec- 
ond or  through  several  such  differential  roller  pairs. 

In  working  the  method  the  arrangement,  represented 
in  the  illustrations  Fig.  79  side  view  and  Fig.  80  plain  is 
used. 

After  the  boiled  cellulose  has  passed  a  sandpang  d  and 
a  wash-drum  f,  it  goes  to  a  draining  arrangement  of  any 
kind,  which  in  the  present  case  consists  of  an  endless  wire 
sieve  a,  and  two  press-rollers  b  and  c,  between  which  goes 
through  the  sieve  a  with  the  cellulose  laying  upon  in  thin 
layer.  The  press-rollers  remove  all  water  from  the  cellu- 
lose, whereby  it  becomes  so  compact  that  it  leaves  the  rol- 
lers in  the  shape  of  leaves  or  sheets  and  in  this  condition 
it  enters  at  once  between  the  rollers  A  and  B,  rotating 
with  unequal  velocity  of  their  circumferences,  where  the 
splinters  or  fibre-bundles  are  separated. 

The  roller  B  is  set  fixed,  while  the  slower  rotating  rol- 
ler A  is  set  in  a  fork  E,  which  turns  in  the  boxes  F.  The 
fork  E  is  adjustable,  in  front  by  a  set  screw  D  and  in  back 
by  set  screws  C.  By  means  of  these  screws,  D  and  C,  the 
roller  A  is  so  adjusted  to  roller  B  that  only  the  splinters 
and  fibre-bundles  are  caught  by  the  rollers,  whereas  the 
single  fibres  pass  free  between.  The  rollers  are  driven  by 
a  pulley,  set  on  the  shaft  of  the  quicker  rotating  roller  B. 
The  roller  A  is  driven  by  the  roller  B  by  means  of  the  gear- 
ing Gr  and  H. 

For  greater  safety  the  cellulose  is  run  through  a  sec- 
ond similar  pair  of  rollers  Al  and  Bl.  By  the  crushing  of 
the  splinters  between  the  rollers  AB  and  Al  Bl,  the  leaf- 
like  continuancy  of  the  cellulose  is  not  injured.  By  em- 
ploying these  differential-roller  pairs,  a  stuff  is  obtained 
uniformly  fine  and  pure. 

2.  Sieve  drum  for  assorting  the  knots  and  coarser 
parts  from  dissolved  cell-stuff: 

The  present  invention  forms  a  sieve-drum  for  assorting 
the  knots  and  larger  particles  from  dissolved  cell-stuff.  It 
is  characterized  by  a  simultaneous  shogging  movement  be- 
sides the  revolving.  To  this  purpose  the  sieve-drum  with 
one  end  set  in  a  traverse,  is  by  lever  and  pallet  wheels  made 
to  have  a  short,  shogging  up  and  down  motion,  while  the 
drum  is  turning.  In  the  following  illustration,  Fig.  81-83, 


THE    MANUFACTURE    OP    CELLULOSE.  165 

are  represented  two  connected  sieve-drums  in  front  and 
side  view  and  in  plane. 

In  a  box-like  frame  B,  open  on  top  rest  the  two  sieve- 
drums  A,  the  mantles  of  which  are  perforated;  each  sieve- 
drum  (fig.  81,  left)  is  closed  by  a  headwall  b,  possessing 
a  large  central  opening  c,  lined  by  a  ring  d,  extending  out- 
ward, and  at  the  same  time  forming  the  front  resting  pin 
for  the  drum.  Th,e  back  end  of  each  drum  is  open.  The 

/A 


Pig.  82. 

back  resting  for  the  drum  is  formed  by  its  driving  shaft  f, 
fastened  in  the  usual  manner  in  the  naves  of  the  heads 
of  the  drum,  and  at  g  (fig.  83)  it  rest  on  the  frame.  The 
shaft  F  receives  its  revolution  by  means  of  the  beveled 
wheels  h  hi  from  the  spindle  i,  which  is  rested  squarely 
in  front  of  the  back  end  of  the  drum  A  in  corresponding 
boxes  of  the  frame  and  carries  the  pallet-wheels  k  and  the 
driving  pully.  The  pallet  wheels  work  against  the  ends  of 


166 


THE    MANUFACTURE    OF    CELLULOSE. 


the  levers  m,  somewhat  extending  above,  which  at  both 
sides  of  the  frame  B  are  set  revolving  about  the  pins  ml 
and  at  its  other  ends  carry  the  traverse  n,  laying  square  in 
front  of  the  other  end  of  the  sieve  drum,  in  which  are  rest- 


K 


Fig.  84. 

ed  and  revolve  the  extending  rings  d  of  the  front  drum 
walls  b.  Two  springs  0,  which  are  braced  against  the 
traverse  n  and  also  against  the  intensions  p  of  the  frame, 
tend  to  lift  the  traverse  with  the  front  ends  of  the  drums. 


THE    MANUFACTURE    OF    CELLULOSE.  167 

By  the  rotation  of  the  shaft  i  the  drums  a  are  caused  to 
revolve  and  at  the  same  time,  by  the  pallet  wheels  k,  the 


o          o          o  o  o          o  o 


u  u 


u  u 


Fig.  85. 


Fig    86. 

levers  m  and  the  springs  0,  the  traverses  n  and  the  front 
ends  of  the  drum  are  caused  to  make  short,  shogging  up 


168  THE    MANUFACTURE    OP    CELLULOSE. 

and  down  motions.  The  dissolved  cell-stuff  flows  through 
the  opening  c  into  the  sieve-drums  and  through  the  holes 
in  the  mantel  of  the  drum  into  the  lower  open  space  of  the 
frame  B,  from  where  it  is  taken  away  through  the  opening 
r  (fig. 8 7).  The  knots  and  coarser  particles  fall  out  at  the 
open  back  end  of  the  sieve-drums. 

3.    ARRANGEMENT  FOR    DERESINATING  THE 
CELL-STUFF. 

The  arrangement  consists  in  the  main  of  a  beater  shaft, 
which  beats  the  cell-stuff  separating  the  particles  of  resin 
from  the  cell-stuff  fibres,  until  a  lather  is  formed,  which 
after  the  liquid  has  come  to  rest,  leaves  upon  it  a  fine  film, 
containing  the  particles  of  resin.  There  are  also  of  one  or 
more  rotating  rollers,  immersed  in  the  liquid,  and  remov- 
ing the  particles  of  resin,  the  latter  adhering  to  the  mantel 
face  of  the  rollers  and  removed  by  scrapers.  The  rollers 
may  be  cooled  or  warmed,  as  desired.  In  the  following  il- 
lustrations fig.  84  represents  a  long  section,  fig.  85  the 
plane  and  Fig.  86  the  sectional  cut  through  the  roller  b. 

In  the  trough  A,  conducting  the  cell-stuff  mass  to  the 
sandfang,  is  arranged  a  beating  spindle  a,  covered  with  a 
cap  d.  The  cell-stuff  flows  from  the  supplying  trough  over 
the  wier  e  to  the  beater  a,  which  so  beats  the  cell-stuff,  that 
a  foam  is  formed,  in  which  the  particles  of  resin  accumu- 
late. Behind  the  beater  the  cell-stuff  flows  over  the  cross- 
wall  f,  behind  which  the  form  disappears  and  leaves  a  fine 
resinous  film  swimming  on  top  of  the  cell-stuff,  which  by 
a  roller  b,  immersed  in  the  liquid  and  slowly  revolving,  op- 
posite to  the  direction  of  the  current,  is  taken  up,  the  par- 
ticles Oi  resin  forming  the  film  adhering  to  the  lower  facr 
of  the  roller.  The  resin  is  then  removed  above  the  liquid 
by  a  scraper  s,  trailing  on  the  roller.  The  scraper  s  rests 
on  the  pin  si  and  at  its  back  end  it  is  provided  with  a  jut- 
ter  s2  to  receive  the  resin.  It  receives,  besides,  by  a  lever  h 
and  a  curved  groove  K,  an  oscillating  motion,  whereby  the 
scraping  off  of  thf  resin  is  facilitated.  The  curved  groove 
K  is  worked  into  the  wave  of  worm-wheel  g,  sitting  on  the 
spindle  of  the  roller  b  and  receiving  its  rotation  from  a 
worm  gl.  The  roller  b  is  arranged  almost  over  the  first 
cross-piece  i  of  the  sandfang.  If  desirable,  several  such 
rollers  C  can  be  arranged  one  after  the  other. 


THE    MANUFACTURE    OP    CEKLULOS-E.  169 


ft, 


Pig.  87. 


Fig.  88. 


170  THE    MANUFACTURE    OF    CELLULOSE. 

A  machine  for  the  same  purpose  is  the  Twirler  of  Carl 
Ziegelmeyer,  described  in  the  Papier  Zeitung,  1895,  and 
represented  in  Figs.  87  and  88. 

It  consists  of  a  cylindrical  mantle.,  to  which  are  screwed 
fast  a  number  of  beating  pins  f,  four  each  in  one  plane,  be- 
tween which  move  the  beating  pins  i,  wedged  in  the  ver- 
tical shaft  g.  The  number  of  the  beating  pins  may  be  in- 
creased or  lessened  as  desired.  The  shaft  is  set  in  a  step 
box  h  and  carries  the  fly  wheel  n,  the  two  stuffing-boxes  d2 
and  e2  are  parts  of  the  cover,  closing  the  cylinder.  The 
driving  is  effected  by  loose  and  fixed  pulley  m  and  beveled 
wheel  jk.  The  two  supports  a  of  the  strong  frame  are  con- 
nected by  a  plate  b,  carrying  the  before-mentioned  foot  box 
h.  The  diluted  stuff,  mixed  up  with  water,  is  by  a  pump 
pressed  through  pipe  dl  into  the  lower  part  d  of  the  cylin- 
der, on  its  way  upwards  being  divided  by  the  beating  pins, 
and  flows  from  the  upper  part  e  off  through  the  pipe  el.  By 
the  above  described  arrangement  of  the  beating  pins  a  twirl- 
ing motion  is  produced  in  the  inner  space  r  of  the  cylinder, 
dividing  the  fibres,  but  leaving  the  hard  particles  unchanged. 
Because  the  cylinder  is  closed  and  over-pressure  exists  in 
it,  the  stuff  while  going  through  is  protected  from  soiling 
and  also  from  lubricating  oil.  A  twirler,  the  cylinder  of 
which  has  a  height  of  1.2  m.  and  a  diameter  of  0.4  m.,  suf- 
fices to  dissolve  about  5,000  kg.  cell-stuff,  boiled  dry,  in  24 
hours,  and  requires  but  1.5  square  meters  of  ground.  The 
consumption  of  power  is  2  to  3  horse-power.  The  twirler 
has  proved  successful  for  eight  years,  in  soda,  as  well  as  in 
sulphite  stuff  factories. 

The  firm  of  Goetjes  &  Schulze,  in  Bautzen,  builds  for 
dissolving  and  fibering  cell-stuff  the  patented  machine  il- 
lustrated in  the  following  five  figures: 

For  this  machine,  after  soaking  and  grinding  the  stuff, 
the  removing  of  the  latter,  as  well  as  of  the  insufficiently 
boiled  particles  and  other  impurities  and  admixtures  is 
effected  in  a  specially  arranged  sievedrum,  whereafter  the 
stuff  is  ground  fine  in  one  or  several  centrifugal  mills.  By 
grinding  fine  is  here  to  be  understood  the  complete  divid- 
ing of  the  fibrebundles,  not  the  crushing  of  the  fibre. 

Fig.  89  is  a  sideview  with  partial  section;  fig.  90  is  the 
head  view  of  the  machine.  The  fig.  91,  92  and  93  repre- 
sent details.  The  stuff  as  discharged  from  the  digester  is 
fed  to  the  machine  at  a,  It  reaches  the  drum  A,  in  which 


THE    MANUFACTURE    OF    CELLULOSE. 


171 


is  turning  a  shaft  al  with  beating  pins  a'2  (fig.  91);  the  drum 
A,  made  of  bronze  or  other  acid  resisting  material,  widens 
a  little  from  the  inlet  towards  the  outlet.  By  the  beating 
and  throwing  action  of  the  pins  -d%,  the  fibrebundles  are 
softened  and  loosened.  By  partion  walls  a3,  set  against 
each  other,  partially  baring  the  cross  space,  the  stuff  can 


Fig.  93 


Fig.  89. 

be  directed  along  a  zig-zag  way  through  the  drum,  where- 
by the  rim  of  the  stuff  is  retarded  and  the  working  by 
the  shaft  a  becomes  more  effective. 

After  the  stuff  has  left  the  drum  A  at  b,  it  is  in  a  pasty 
condition  carried  to  the  centre  of  the  centrifugal  mill  B. 


172 


THE    MANUFACTURE    OF    CELLULOSE. 


In  this  (fig.  92),  which  is  of  the  usual  arrangement,  oppo- 
site the  fixed  head  bl  is  set  On  shaft  b2;  the  rotating  head 
1)3,,  both  heads  are  set  with  beating  pins  of  square  cut.  The 
object  of  this  centrifugal  mill  is  the  previous  grinding  of 
the  stuff,  as  against  the  grinding  fine,  to  be  described  later 
on.  It  is  the  purpose  to  continue  the  softening  and 


Figs.  90,  91,  92. 

loosening,  commenced  in  A,  until  the  dividing  of  the  fibre- 
bundles,  but  most  of  all  to  bring  the  stuff  in  a  condition 
in  which  the  knots  and  other  impurities  or  admixtures  are 
separated  from  the  cellstuff,  without  being  ground. 

This  separating  of  the  knots,  etc.,  is  effected  in  a  sieve- 


THE    MANUFACTURE    OF    CELLULOSE.  173 

drum,  C,  into  which  the  stuff  enters  through  the  bent  pipe 
c,  starting  at  the  circumference  of  B. 

The  hollow  neck  cl,  at  the  left  side  of  the  drum,  carries 
a  disk  c2,  with  which  the  left  end  of  the  drum  is  resting 
o --1  the  friction  and  guide-rollers,  c3,  of  which  one  is 
wedged  on  thr  driving  pin  c4.  In  similar  manner  the  right 
end  of  the  drum  with  a  disk  c5  of  wedge-like  shape  is  rest- 
ing on  grooved  rollers  c6.  As  perceivable  from  fig.  90  the 
axis  of  the  drum  has  an  oblique  position,  being  lowered 
towards  the  entrance  end  of  the  left  side.  So  far  as  the 
exit  end  the  sieve  mantel  is  immersed  in  a  trough  cl,  filled 
with  water  and  stuff.  The  bent  pipe  c  is  covered  inside 
the  drum  by  a  cap  c7  in  such  manner  that  the  stuff  cannot 
be  thrown  through  the  drum  along  the  direction  of  the 
axis,  but  must  leave  c  in  a  radial  direction.  The  mantle 
of  the  drum  is  fitted  inside  with  a  winding  alley  c8  (fig 
93);  by  a  pipe  c9.  Water  can  be  injected  when  necessary. 

Whilst  the  stuff  conducted  to  the  sieve  drum  through 
pipe  c  is  slowly  moved  on  by  c8,  the  sufficiently  divided 
particles  pass  through  the  sieve  mantle  into  the  water, 
while  the  knots  and  such  other  matter  are  carried  along 
by  the  spiral  c8.  The  position  of  the  axis  of  the  drum  to 
the  level  of  the  water  causes  the  knots  to  keep  swimming 
and  not  to  be  in  the  way  of  the  passage  of  the  stuff  parti- 
cles towards  Cl;  until,  nearing  the  end  of  the  drum,  they 
reach  the  mantle  and  are  by  the  spiral  carried  to  the  shoot 
C3.  In  Cl  besides  the  pure  stuff  are  now  also  contained 
the  heavy  impurities,  which  pass  the  sieve  mantle;  these 
sink  to  the  bottom,  while  the  stuff  flows  over  C2  through 
the  bent  pipe  d  into  the  centre  mill  D  for  grinding  fine,  i. 
e.,  for  thorough  separation  of  the  fibres.  Through  the 
pipe  dl  water  can  be  supplied  to  this  centrifugal  mill, 
should  it  become  necessary.  Its  inner  arrangement  corre- 
sponds to  that  of  the  already  described  centrifugal  mill  B. 

Also  based  on  the  principle  of  centrifuging,  Hagemann 
&  Co.  have  built  a  patented  wet,  centrifuge  with  circulat- 
ing vessel  for  milling  cellstuff  after  digesting.  This  cen- 
trifuge is  arranged  over  a  cylindrical  pipe  g,  the  upper 
edge  of  which  is  formed  into  a  ring-like  closed  box  c,  the 
cover  of  which  also  answers  the  fixed  peg-ring  of  th( 
centrifuge.  The  shaft  1,  which  carries  the  upper,  rotating 
peg-disk  f  and  the  axis  of  which  falls  together  with  that 
of  the  pipe  g,  goes  through  the  bottom  of  the  circulating 


174  THE    MANUFACTURE    OF    CELLULOSE. 

vessel  and  is  consequently  intended  to  be  driven  from  be- 
low. The  pegs  d  of  the  fixed  ring  are  provided  with  axial 
bore  almost  up  to  the  point,  communicating  with  the  ring 
box  c.  This  is  connected  with  a  water  supply  through  a 
pipe  b,  from  which  the  water  enters  the  bores  of  the  pegs 
under  pressure.  From  these  the  water  is  forced  through 
small  holes,  divided  along  the  pegs  and  against  the  pegs  e 
of  the  revolving  disk  f.  To  prevent  the  water  from  get- 
ting outside  along  the  face  of  the  disk  f,  it  is  of  advantage 
to  cut  grooves  in  the  rotating  disk  f,  over  the  peg-ring  of 
the  fixed  disk,  i.  e.,  over  the  water  outlets,  in  order  that  the 
water  may  be  turned  off  downwards  and  led  between  the 
pegs.  These,  with  sufficient  velocity  of  rotation,  atomize 
the  water  and  throw  it  out  with  great  force  tangentially; 
whereby  it  acts  with  suction  similarly  to  the  well  known 
ejectors.  The  stuff  standing  in  pipe  g  but  little  below  its 
upper  edge,  is  therefore  sucked  up,  fed  to  the  centrifuge 
and  by  it  filtered  and  mixed.  The  stuff  now  thrown  out 
by  the  centrifuge,  with  great  force,  is  with  advantage 
thrown  against  a  concentric  wall,  whereby  it  suffer?  fur- 
ther division.  From  this  wall  the  stuff  f  then  flows  either 
directly  or  through  a  trough  or  channel  into  a  suitable 
vessel,  which  communicates  with  the  lower  end  of  the  pipe 
g.  In  this  manner  a  circulation  is  obtained  which  makes 
it  possible  to  run  the  stuff  through  the  centrifuge  as  often 
as  desired. 

When  the  stuff  at  the  same  time  is  to  be  washed,  a,s  is 
always  desired  in  the  milling  of  cellstuff,  it  is  practical  to 
give  the  circulating  vessel  the  form  of  the  hollander  tank, 
in  which  there  are  then  arranged  the  washdrums  in  the 
customary  manner.  When  washing  the  water  can  be  con- 
tinuously supplied  through  the  lower  pegs  of  the  centri- 
fuge, whereas  when  only  fibring  or  mixing  of  the  stuff  is  in 
question,  the  water  is  but  supplied  to  the  pegs  only  until 
the  stuff  is  sucked  up,  when  the  water  supply  is  then  shut 
off. 

The  described  centrifuge  is  arranged  in  the  middle  of  a 
double  hollander  tank  U  U.  The  hollander  box  and  the 
frame  of  the  centrifuge  are  made  of  cement  and  only  the 
working  parts  and  valves,  etc.,  have  to  be  made  of  metal. 

When  the  circulating  vessel  U  is  sufficiently  filled  with 
stuff,  the  shutter  a  is  opened.  The  water  now  enters  from 
the  pipe  line  b  into  the  ring-like  box  c,  and  from  there  in 


THE    MANUFACTURE    OF    CELLULOSE. 


17& 


176 


THE    MANUFACTURE    OF    CELLULOSE. 


to  the  pegs  d.  From  these  the  water  spouts  through  the 
already  mentioned  small  holes  against  the  pegs  e  of  the  ro 
tating  disk  f,  which  atomize  and  throw  it  out;  the  stuff 
thereby  sucked  up  rises  in  pipe  g,  passes  the  centrifuge  and 
is  thrown  against  the  walls  of  the  ring-channel  h.  From 
this  channel,  on  which  are  formed  four  saddles  i  for  thj 
equal  distribution  of  the  stuff,  the  latter  flows  through  the 
four  openings  k  into  the  outer  compartments  of  the  three- 
parted  hollander  tank.  The  arrows  mark  the  further  cir- 
culation of  the  stuff  until  it  reaches  again  the  centrifuge. 
A  simple  arrangement  for  the  separating  of  the  cellstufl 
from  the  waste  leach  has  been  patented  by  George  Setter 
•and  Franklin  Emig,  of  Spring  Forge,  Penn.  (American 
patent  No.  514,780.)  It  is  described  as  follows: 


Fig.  96. 

To  separate  the  cellstuff  from  the  waste  leach  as  com- 
pletely as  possible  without  employing  wash  water,  the  cell- 
stuff  coming  from  the  digester,  saturated  with  leach,  is 
run  into  the  funnel  B,  from  where,  after  opening  a  slide, 
it  falls  on  an  endless,  penetratable  ribbon  c,  (for  example 
a  sieve,)  which  carries  it  through  one  or  more  pairs  of  press 
rollers  D  D  and  then,  in  dry  condition,  into  the  space  G. 
In  this  space  it  is  so  much  diluted  by  water,  supplied  by 
the  channel  e,  that  it  can  be  pumped  to  any  place  desired 
for  further  working.  The  waste  leach  accommulates  in 
the  compartment  F  without  becoming  diluted  at  all. 

For  milling  the  boiled  cellulose,  Karl  Kellner  had  pat- 


THE    MANUFACTURE    OP    CELLULOSE. 


177 


ented  under  Am.  pat.  No.  489,079,  the  following  described 
machine: 

By  this  invention  the  knots,  undissolved  in  boiling,  are 
prevented  from  becoming  disintegrated  and  getting  into 
the  paper.  The  case  of  the  machine,  as  seen  in  Fig.  98,  is 


Fig.  98. 

almost  elliptical  in  cross  section  and  conical  in  such  man- 
ner that  from  the  end  where  the  cellstuff  is  introduced  (g) 
it  becomes  wider  towards  the  other  end.  The  dividing  of 
the  cellstuff  is  effected  by  beaters  d  and  dl,  which  are  fast- 


178 


THE    MANUFACTURE    OF    CELLULOSE. 


ened  to  the  naves  wedged  to  the  shafts  c  and  cl  and  with 
these  naves  form  one  piece  each.  The  beaters  of  the  one 
shaft  move  between  the  beaters  upon  the  other  shaft,  with- 
out touching  them,  so  that  the  knots  are  left  uncrushed. 
Corresponding  to  the  conical  form  of  the  case,  the  beaters 
become  longer  from  one  end  to  the  other.  To  facilitate  the 
discharging  a  pipe  h  is  arranged  opposite  the  exit  pipe  k, 
through  which  the  water  is  supplied.  The  cellstuff  is  in- 
troduced in  the  condition  of  a  thick,  half-dry  dough.  The 
two  shafts,  c  and  cl,  are  driven  in  opposite  directions  by 
means  of  pulleys  f  and  fl. 

Another  arrangement  for  the  milling  of  boiled  wood  and 
the  separating  of  knots  from  the  stuff  is  that  of  Phillip 
Dieiz. 


Fig.  99. 

The  arrangement  consists  mainly  of  the  conical  drum 
T,  inclined  on  one  side.  It  has,  where  its  diameter  is 
smallest,  the  inlet  opening  P  for  the  boiled  wood  ;at  the 
other  end,  where  the  diameter  is  the  largest,  the  outlet  R 
for  the  pasty  stuff  and  also  an  opening  for  cleaning  K  are 
arranged.  The  narrow  part  of  the  drum  is  lined  with  a 
pad  or  cover  H,  of  rubber,  felt  or  other  material.  In  the 
wider  part  of  the  drum  are  arranged  three  copper  water 
supply  pipes  z. 

To  the  shaft  W  of  the  drum  are  fitted  the  spokes  N,  along 
a  spiral  line;  the  latter,  together  with  the  shaft,  are  cov- 
ered with  a  pad  of  rubber  in  such  manner  that  between 
the  lining  of  the  drum  and  the  ends  of  the  spokes  a  free 


THE    MANUFACTURE    OF    CELLULOSE.  179 

space  is  left.  At  the  outlet  E  stops  are  fixed  adjustable 
to  make  a  stopping  of  the  stuff  possible.  Further,  for  fur- 
ther division,  a  pro-sorting  box  S  is  arranged  with  the 
sprinkle  pipes  Q  and  the  outlet  openings  L. 

The  boiled  wood,  which  is  conducted  from  the  digesters 
or  storage  room  to  the  inlet  P,  is  worked  dry  in  that  part 
of  the  drum  in  which  is  the  padding  H.  By  the  latter  as 
well  as  by  the  padding  of  the  shaft  and  spokes  is  prevent- 
ed the  crushing  of  the  hard  particles  of  wood  and  of  the 
knots. 

The  spokes  N  push  the  stuff  ahead  in  such  manner  that 
each  of  them  works  the  stuff  ahead  to  the  next  one.  In 
order  to  be  able  to  change  the  number  of  revolutions  of 
the  spokewheel  quickly,  step-pulleys  are  employed.  While 
in  the  upper  narrow  half  of  the  drum  the  soft-boiled  parts 
are  separated  from  the  knots,  in  the  lower  wet  part,  the 
flocks  are  completely  fibred  and  disssolved.  The  stuff 
passes  gradually  over  the  wier  and  then  receives  liberal 
addition  of  water.  In  the  pro-sorting  box  S  the  knots,  as 
well  as  unboiled  particles  of  wood  and  other  admixtures, 
next  settle  down.  After  the  fibres  still  adhering  to  the 
knots  are  removed  by  the  sprinklers,  before  they  can  set- 
tle to  the  bottom,  the  stuff  is  finally  conducted  to  a  trough 
or  sandfang  of  the  customary  construction. 

After  the  single  rolls  are  wrapped  in  good  packing,  pa- 
pered and  corded,  or  packed  otherwise,  the  product  is 
ready  for  shipping,  but  care  must  be  taken  that  before 
packing  sufficient  samples  are  taken  that  the  amount  of 
moisture,  which  in  shipping  goods  in  moist  condition 
form  an  important  item,  and  often  causes  differences,  can 
be  determined  as  closely  as  possible. 

The  working  of  moist  cellulose  is  very  convenient  for 
the  paper  manufacturer.  Lately,  however  moist  cellulose 
factories  have  provided  for  drying  cylinders  and  thus 
formed  the  wet  machine  into  a  regular  paper  machine,  able 
to  produce  absolutely  dry  stuff  or  almost  dry,  of  about  80 
to  90°,  and  thus  to  save  freight  expense  or  to  be  able  to 
sell  the  cellulose  in  far-off  markets  with  profit.  Fortun- 
ately the  drying  is  not  of  much  disadvantage  to  the  paper 
manufacturer,  although  it  is  claimed  the  fibre  loses  some 
of  its  firmness;  but  it  dissolves  easily  in  water  and  offers  the 
advantage  that  it  can  be  kept  in  store  for  any  length  of 


180  THE    MANUFACTURE    OF    CELLULOSE. 

time  without  danger  of  getting  musty,  as  happens  easily 
with  moist  straw  stuff. 

Some  factories,  shipping  the  cellulose  in  moist  condi- 
tion, who  have  to  serve  their  customers  a  specially  pure 
product,  after  having  finished  rolling  are  doing  another 
sorting  by  repeated  off  and  up  rolling,  which  is  done  with 
a  small  apparatus,  represented  in  Fig.  100  and  101: 

An  upright  frame  A  carries  several  boxes;  in  the  lower 
one  is  set  a  spindle,  on  which  is  fitted  the  roll  B  of  cellu- 
lose to  be  assorted;  above  are  arranged  two  guide  rollers  c 
and  d  and  further  up  a  strong  wooden  roller  E  (200  mm 
diameter)  which  by  a  belt  from  the  transmission  is  slowly 
turned  (8  revolutions  per  minute).  Over  it  are  arranged 
two  forklike  slide  boxes,  in  which  is  laid  the  roller  on 
which  the  cellulose  to  be  sorted  is  rolled  up.  After  a  roll 
of  cellulose  is  put  in  below,  and  drawn  over  the  guide  rol- 
lers and  the  wooden  roller  E  and  around  the  roller  f,  the 
winding  up  will  start  above.  The  cellulose  breadth,  as  a 
rule  1  meter. wide,  is  slowly  moved  upward  in  the  direc- 
tion of  the  arrow  and  the  roll  B  is  gradually  rolled  off.  At 
both  sides  of  the  frame  girls  stand  to  pull  out  all  impuri- 
ties or  larger  splinters  with  their  fingers,  while  the  ma- 
chine is  going.  When  the  girls  are  careful  the  result  of 
the  sorting  is  good,  but  the  expense  in  wages  is  not  small, 
several  sorting  frames  are  necessary  (about  three  for  every 
digester)  and  besides  the  loss  of  stuff  amounts  to  15  per 
cent,  which,  however,  is  used  again  along  with  the  second 
quality. 

All  those  cellstuff  factories,  which  work  for  export,  are  . 
required  to  perforate  the  dry  cellstuff  boards,  that  they 
are  not  taken  for  real  pasteboard  by  the  revenue  officials, 
and  as  such  taxed  higher.  This  was  formerly  effected  by 
arranging  a  pipe  under  the  sieve,  by  which  periodically 
strong  jets  of  water  were  sent  from  below  through  the 
stuff-mass.  Thereby,  however,  strong  edges  were  unfor- 
tunately formed  around  the  perforations,  which  in  press- 
ing caused  unequal  states  of  dryness. 

Because  the  government  now  requests  regular  perfora- 
tion, different  apparatuses  have  been  constructed. 

One  of  them,  built  and  patented  by  the  Kuehule  ma- 
chine factory  in  Frankenthal,  is  described  and  illustrated 
in  the  Papier  Zeitung. 

By  this  arrangement  the  perforating  of  the  paste  is  done 


THE    MANUFACTURE    OF    CELLULOSE.  181 

on  the  wet  machine  in  such  manner  that  the  cellstuff  can- 
not be  taken  for  pasteboard  by  the  revenue  authorities. 
The  dies  and  sinkers,  which  are  fixed  to  a  frame  swinging 
around  an  axis,  follow  the  finished  sheet  of  dry  stuff,  while 
perforating  and  there  at  once  return  to  starting  position. 


IE 


fl 


EE 


U 


D 


=Lt 


Figs.  100-101. 

As  advantages  of  this  arrangement  are  claimed: 
First. — Faultless  perforation,  i.  e.,  no  injuring  of  the 
good  appearance  of  the  stuff  by  the  perforating;  second, 


182  THE    MANUFACTURE    OF    CELLULOSE. 

preservation  of  the  expensive  transport  sieves,  against  the 
method  of  perforating  by  water  jets  and  others;  third, 
convenient  application  of  the  arrangement  to  any  machine. 

A  much  more  simple  arrangement  for  perforating  cell- 
stuff  board  is  the  one  of  H.  Fullner  in  Warmbrunn.  An 
upper  roller  is  provided  with  pins,  which  fit  into  corre- 
sponding holes  of  the  lower  roller  and  cut  just  as  many 
holes  into  the  stuffboard.  The  pins  are  edged  on  the  outer 
face,  in  order  to  make  an  incision  and  not  tear  through. 
A  scraper,  laying  against  the  upper  roller,  holds  back  the 
shreds  possibly  adhering.  It  may  be  conveniently  taken 
off  the  board  of  stuff  if  necessary  and  is  provided  with 
notches,  which  permit  the  pins  to  pass. 

The  upper  roller,  with  the  pins  of  hard  steel  set  in,  is 
of  cast  iron,  whereas  the  counter  roller  with  the  holes  is 
made  of  steel  tube  so  that  the  edges  of  the  holes  form  steel- 
cutters,  working  together  with  the  steel  pins.  The  per- 
forator can  be  made  so  that  all  four  sides  of  the  pin  cut, 
and  the  pieces  of  cell-stuff  board  cut  out,  fall  into  the  hol- 
low space  of  the  lower  roller;  they  accumulate  there,  until 
pushed  to  the  ends,  where  they  drop  through  four  round 
holes  into  the  wooden  boxes  standing  under. 

If  the  square  clippings  of  cell-stuff  should  stick  to  the 
cell-stuff  pieces,  only  three  sides  of  the  pins  are  made  to 
cut,  so  that  on  its  back  side  the  clippings  are  left  con- 
nected with  the  piece.  The  piece  is  then  passed  under  a 
strike-board,  which  turns  the  clippings  over  and  by  rol- 
lers they  are  so  pressed  against  the  drying  cylinders  that 
the  turned  over  clipping  will  stick  to  the  piece  and  leave 
the  holes  entirely  open. 

The  perforator  is  mostly  connected  in  the  paper  ma- 
chine between  pressers  and  dryer. 

Many  factories  sell  part  of  their  production  in  bleached 
state  and  then  up  to  rolling  up  and  assorting  treat  the  cell- 
ulose in  the  same  manner  as  described  above,  after  which 
an  ordinary  bleaching  hollander  is  employed.  This  should 
be  of  at  least  300  kilos  hold  of  stuff.  Let  it  first  be  al- 
most filled  with  water,  warmed  by  steam  and  then  from  a 
box  standing  near  the  hollander,  and  holding  exactly  the 
quantity  of  the  chlorine  water  necessary  to  be  added, 
(1J  cubic  meter  for  above  quantity  of  stuff)  the  chlorine 
is  let  into  the  hollander.  Then  is  introduced  the  stuff, 
the  damp  cellulose,  wound  up  in  rolls.  In  about  three 


THE    MANUFACTURE    OF    CELLULOSE.  183 

hours  the  bleaching  process  is  finished  and  this  is  follow- 
ed by  washing,  which  requires  one  hour,  and  then  the 
bleached  cellulose  can  be  let  into  the  stuff-tanks,  from 
where  it  goes  to  the  before  mentioned  drainer  and  is  wound 
up  again  in  rolls. 

For  several  years  there  has  been  used  for  the  bleaching 
of  cell-stuff  a  hollander  which  varies  from  the  ordinary 
form,  but  possesses  highest  efficiency,  because  it  effects 
closest  and  quickest  mixing  of  the  stuff  with  the  bleach 
water  and  with  the  utmost  cleanliness.  It  is  the  wash- 
bleach-hollander  built  and  patented  by  Emil  Nacke,  which 
is  made  in  large  dimensions:  9  m.  length  and  4J  m.  width, 
inside  measure,  and  holds  1400  kgr.  stuff. 

The  moving  and  mixing  of  the  siuff  is  not  done  by  pad- 
dle wheel,  but  by  a  turbine-like  wheel  of  650  millimeters 
diameter,  which  is  arranged  at  the  bottom,  makes  200  rev- 
olutions p-er  minute  and  is  driven  by  a  belt  from  below,  so 
that  of  the  driving  mechanism  nothing  at  all  can  be  seen. 
By  this  wheel  the  stuff  is  moved  around  noiselessly.  The 
current  is  so  strong  that  the  stagnation  of  the  stuff  in  the 
corners  is  entirely  obviated  and  the  use  of  stirrers  is  unnec- 
essary. Except  with  the  walls,  which  are  lined  with  white 
tiles,  the  stuff  comes  in  contact  with  nothing  but  phosphor 
bronze  and  glass,  which  substances  are  resistant  against 
acid  and  chlorine  and  hence  clean.  The  wheel  f,  which  ro- 
tates above  the  bronze  plate  a,  is  of  phosphor  bronze  and 
the  plates  b  and  c  are  of  glass.  The  stuff,  moving  in  the 
hollander  towards  the  wheel,  is  by  the  inclined  glass  plate 
b  turned  downwards,  then,  as  the  arrows  show,  sucKeci  off 
by  the  wheel  and  after  going  through  the  wheel  leaves  at 
its  circumference  m  current!  spreading  in  the  form  of  a 
fan.  The  stuff  leading  the  wheel  toward  the  front  pro- 
duces a  strong  undercurrent  close  to  the  bottom  of  the  hol- 
lander, by  which  all  settling  of  stuff  at  the  bottom  and  in 
the  corners  is  prevented.  The  stuff  leaving  towards  the 
glass  plate  b,  is  by  this  and  the  glass  plate  c,  as  the  arrows 
indicate,  also  turned  towards  the  front  and  forms  together 
with  the  under  current  the  strong  draft  of  this  hollander. 
The  difference  between  the  levels  of  the  stuff  in  front  and 
behind  the  plate  b  amounts  to  three-fourths  meter  and  by 
this  in  fact  is  conditioned  the  lively  current  of  the  hol- 
lander. The  mixture  produced  by  the  hollander  is  al- 


1S4  THE    MANUFACTURE    OF    CELLULOSE. 

ready  a  perfect  one  after  once  going  through,  so  that  the 
chlorine  water  introduced  at  one  place,  after  going  but 
once  through  the  wheel,  is  mixed  quite  uniforniily  with 
the  stuff.  In  the  same  even  manner  the  heating  of  the 
stuff  is  done  by  a  current  of  steam  let  in;  the  temperature 
of  the  stuff,  even  in  the  largest  hollander,  is  thereby  in- 
creased about  the  same  all  over;  so  that  the  temperature 
can  be  made  the  most  favorable  for  the  bleaching  process, 
without  part  of  the  stuff  becoming  heated  the  fraction  of 
a  degree  above  or  below. 

The  Nack  hollander  has  inside  of  the  tank  no  hidden 
corners  and  nooks,  every  part  of  it  lays  entirely  open  to 
the  eye,  after  the  stuff  is  let  off.  This,  together  with  the 
clean,  acid  and  chlorine  resisting  material,  is  an  impor- 
tant advantage,  where  the  production  of  the  purest  stuff 
is  the  question. 

Because  the  hollander  is  also  used  for  washing,  Nacke 
also  uses  a  washdrum,  not  the  ordinary  one,  however,  but 
an  aspirator  wash-drum  of  his  own  system,  which  works 
so  easy  that  it  does  not  require  special  power,  but  is  driven 
by  the  motion  of  the  stuff.  Gearing  and  belts  with  their 
uncleanliness  are  therefore  dispensed  with.  This  wash- 
drum  furthermore  also  washes  much  more  energetically 
than  the  ordinary  dipping  washdrum  and  has  over  this 
the  other  advantage  that  the  sieve  lining  last  twice  as 
long  and  the  loss  of  fibre  in  washing  is  much  less. 

The  arrangement  is  as  follows:  The  washdrum  is  a 
simple  cylinder,  provided  with  a  fine  sieve  lining,  turns 
loosely  on  a  hollow,  fixed  shaft,  on  which,  inside  of  the 
drum,  are  set  three  aspirator  pipes,  open  below,  turned 
downward  into  the  water.  Because  the  shaft  is  fixed 
these  aspiidtor  pipes  maintain  their  downward  position. 
Outside  of  the  hollander  wall  is  screwed  to  the  hollow 
shaft  a  long  fill  tube,  dipping  into  a  box,  in  which  is  a 
partition  of  adjustable  height,  permitting  the  regulation 
of  the  quantity  running  off.  The  deeper  the  weir  is  set 
the  stronger  the  drum  will  suck.  To  complete  and  main- 
tain the  vacuum  a  small  aspirator  is  used,  it  is  driven  by 
water,  which  is  supplied  by  a  hose  under  four  meters 
pressure  or  more.  The  hose  is  20  mm.  wide,  but  the 
bore  in  the  aspirator  is  only  5  mm.,  the  consumption  of 
water  is  consequently  very  small.  Through  a  second  rub- 
ber hose  the  consumed  water  runs  off  into  a  tank.  The 


THE    MANUFACTURE    OP    CELLULOSE. 


185 


first  water-supplying  hose  must  be  long  enough  so  that 
the  drum  can  be  entirely  lifted  out  when  no  washing  is  to 
be  done.  In  the  other  case,  the  washdrum  is  let  down 
by  a  set-wheel,,  so  that  it  immerses  into  the  stuff,  displaces 
it  somewhat  and  lets  the  dirt-water  penetrate  through  the 
sieve-lining  into  the  interior.  The  rotating  stuff  at  once 


Fig.  102. 

sets  the  drum  into  revolving  motion  so  that  it  is  con- 
tinuously offering  a  face  to  the  penetrating  water.  The 
aspirating  apparatus  is  set  working  by  opening  the  water- 


186  THE    MANUFACTURE    OF    CEL/LULOSE. 

supply  valve,  a  vacuum  is  caused  in  the  hollow  stuff,  the 
dirt-water  is  raised  up  through  the  aspirating  pipes,  is 
received  oy  the  hollow  shaft  and  conducted  away  by  the 
outlet  pipe  attached  to  it,  and  because  this  is  emersed  in 
the  box  filled  with  water,  a  continuous  aspirating  of  the 
dirt-water  is  affected.  . 

Although  the  method  is  not  yet  introduced  in  cellulo? 
factories,  the  electric  bleaching,  worked  out  by  E. 
Hermite  could  be  employed  in  place  of  bleaching  with 
chloride  of  lime.  This  is  claimed  to  yield  a  saving  of  at 
least  50  per  cent  in  bleaching  material.  With  wi-.Ier  ex- 
tension of  the  latest  Kellner  method  of  producing  cell- 
stuff  by  means  of  the  electric  current^  this  bleach  would 
certainly  not  be  necessary  because  as  heretofore  mention- 
ed, by  this  a  snow-white  stuff  is  already  produced.  But 
for  the  sake  of  completeness  this  bleaching  method 
should  be  mentioned.  It  is  based  on  the  following:  When 
a  solution  of  chloride  of  magnesia  of  5  per  cent,  chloride 
of  magnesia  and  95  per  cent,  water  is  electrolized  in  a 
convenient  arrangement,  water  and  chloride  of  mag- 
nesia are  simultaneously  decomposed.  The  chlorine  sepa- 
rated from  the  chloride  of  magnesia,  and  the  oxygen, 
from  the  water,  under  the  influence  of  the  electrolysis, 
combine  at  the  positive  pole  and  produce  a  loose  chlorine- 
oxygen  combination,  which  is  possessed  of  strongly  de- 
colorizing quality. 

The  hydrogen  and  the  magnesium  go  to  the  negative 
pole.  This  decomposes  water  and  forms  magnesium  oxide, 
while  hydrogen  is  set  free.  When  vegetable  fibre  is 
brought  into  such  liquid,  the  oxygen  combines  with  the 
coloring  substance  and  oxydizes  it;  the  chlorine  combines 
with  the  hydrogen  and  forms  hydrogen-chloride,  which 
again  goes  into  combination  with  the  magnesia  in  the 
liquid  and  reproduces  anew  the  chloride  of  magnesia.  This 
circulation  is  repeated  as  long  as  the  electric  current,  is 
acting  on  the  solution,  holding  the  colored  substance.  To 
a  perfect  circulation  of  this  kind  are  therefore  necessary. 
First,  electric  current;  second,  chloride  of  magnesia1 
third,  water;  four,  coloring  substances. 

Two  of  these  elements  serve  to  destroy  the  coloring  suV> 
stances;  viz.,  the  electric  current,  or,   what  amounts  1o 
the  same  thjng,  the  acting  force  and  the  water.     Tlie 
chloride  of  niagnesia  serves  continuously;  only  a  simplt 


THE    MANUFACTURE    OF    CELLULOSE.  187 

moving  of  the  molecules  takes  place  and  the  chlorine  acts 
as  a  conductor,  bringing  the  oxygen  produced  to  the  col- 
oring substances.  It  has  been  proved  that  the  electric 
method  exercises  a  quicker  decolorizing  action  than  com- 
mon chloride  of  lime. 

In  general  Hermite  points  out  the  advantages  of  his 


Fig.  103. 

method  as  follows:  First,  it  permits  every  bleacher  to  pro- 
duce for  himself  the  discoloring  substances  and  this  with- 
out noticeable  interruption  of  his  work;  second,  the  de- 
colorizing means  is  pure  and  does  not  leave  a  residue; 


188  THE    MANUFACTURE    OF    CELLULOSE. 

third,  it  possesses  considerably  greater  decolorizing  effect 
than  chloride  of  lime;  fourth,  its  action  on  fibres  ensues 
quicker,  is  more  uniform  and  is  less  injurious;  fifth,  its 
employment  means  considerable  saving  of  money;  sixth, 
the  cost  of  production  is  uniform. 

In  this  method  only  that  part  of  chloride  of  magnesia 
is  lost  which  is  contained  in  the  danjp  stuff  after  press- 
ing. At  40  per  cent  dryness  there  are  to  be  considered 
40  kilos  of  stuff  and  60  kilos  of  water;  then  for  100  kilos 
of  dry  stuff  150  kilos  of  chloride  of  magnesium  solution  gets 
lost,  containing  10J  kilos  of  chloride  of  magnesia. 

The  apparatuses  for  electric  bleaching  are  built  by 
Paterson  and  Cooper  in  London.  The  electrolysor  con- 
sists of  a  cast  iron  vessel,  in  the  lower  part  of  which  is 
let  in  a  perforated  pipe,  provided  with  a  zinc  cock, 
through  this  pipe  the  chloride  of  magnesium  solution 
enters  the  apparatus;  its  upper  edge  is  flattened  out,  re- 
ceives the  overflowing  solution,  and  conducts  it  to  another 
vertical  pipe.  This  second  serves  to  create  the  circula- 
tion of  the  solution.  Along  the  length  of  the  electro- 
lysor lay  two  shafts,  to  which  are  fixed  disks  of  zinc; 
these  disks  of  zinc  are  the  negative  electrodes  and  move 
in  slow  rotation.  Intermitted  with  each  negative  elec- 
trode is  set  a  positive  electrode;  the  active  surface  of 
which  consists  of  platinum  netting  held  in  a  frame  of 
hard  rubber.  The  upper  part  of  the  platinum  netting  is 
soldered  to  a  lead  body  and  completely  isolated.  By  means 
of  this  lead  body  every  positive  electrode  is  connected 
with  the  copper  circuit,  conducted  through  the  electroly- 
sor; the  contact  is  effected  by  a  female  screw.  During 
working  any  electrode  can  be  taken  out,  without  any  in- 
terupting  of  the  process  in  the  apparatus.  In  connection 
with  the  copper  conductor  to  which  the  positive  electrodes 
are  fastened,  is  the  positive  pole  of  the  dynamo  machine. 
The  electric  current  now  distributes  itself  upon  all  plati- 
num electrodes,  goes  through  the  liquid  in  the  zinc 
disks,  i.  e.,  negative  electrodes  and  connects  by  means 
of  the  galvanic  cast  iron  vessel  with  the  negative  pole  of 
the  dynamo  machine.  For  the  purpose  of  keeping  them 
clean  elastic  scrapers  of  hard  rubber  are  arranged  at  the 
positive  electrodes,  tightly  lying  against  the  zinc  disks. 
These  they  keep  clean  of  every  deposit  while  slowly  ro- 
tating. The  apparatus  can  be  emptied  by  opening  a  valve. 


THE    MANUFACTURE    OF    CELLULOSE. 


189 


When  several  apparatuses  are  used,  they  are  set  for 
intensity,  i.  e.,  the  positive  pole  of  the  first  is  connected 
with  the  negative  pole  of  the  second,  and  so  on.  An  elec- 
tric current  of  1,000  to  1,200  ampires  is  generally  used  to 
work  the  electrolysor. 

Each  apparatus  substitutes  the  decolorizing  action  of 
about  125  kilos  of  English  chloride  of  lime  of  about  33 
per  cent  of  chlorine  in  24  hours  of  continuous  work  and 
requires  about  8-|  horse  power.  I'he  inventor  guarantees 
for  every  electrolysor  of  1,000  ampires  current  the  substi- 
tution of  the  bleaching  power  of  100  kilos  chloride  of 
lime,  and  an  expense  for  power  of  9  horse  power  on  the 
pulley  of  the  dynamo  machine  in  24  hours  work. 


Fig.  104. 

To  represent  the  circulation  arranged  in  electric  bleach- 
ing, is  the  shematic  figure,  104: 

.From  the  vessel  A  the  solution  of  chloride  of  magnes- 
ium, to  which  some  magnesia  is  added,  enters  in  to  the 
electrolizer  B  and  falls  from  there  into  the  bleach  holland- 
er  C  where  the  decolorizing  of  the  stuff  tobe bleached  takes 
place.  The  wash  drum  D  conducts  the  spent  solution  into 
the  vessel  I  and  the  centrifugal  pump  J  carries  it  back  to 
the  original  starting  point  A.  By  means  of  this  steadily 
maintained  circulation  the  solution  continuously  keeps  up 


190  THE    MANUFACTURE    OF    CELLULOSE. 

the  same  effectiveness.  When  the  stuff  is  properly  decol- 
ored it  is,  together  with  the  solution  still  contained  in  the 
hollander,  let  off  into  the  vessel  E,  where  the  after-bleach 
takes  place;  when  this  is  finished,  the  stuff  goes  over  the 
wet  press  G,  where  it  is  deprived  of  its  water.  The  solu- 
tion running  off  G  is  caught  in  the  tank  H,  let  into  the 
main  tank  I,  and  from  there,  by  means  of  the  pump  J,  re- 
turned to  the  tank  F.  In  special  cases,  when  for  instance 
difficultly  bleachable  stuffs  are  to  be  bleached,  it  is  advisa- 
ble to  previously  let  the  solution  circulate  for  some  time 
between  the  two  vessels  F  and  J;  also  the  apparatus  B.  The 
solution  becomes  thus  more  effective  and  the  stuff  is 
bleached  quicker.  It  may  be  mentioned  that  during 
bleaching  an  excess  of  free  magnesia  is  ever  required  in  the 
solution  of  magnesia  chloride  to  maintain  the  latter  neu- 
tral. It  can  be  made  at  home  in  the  following  manner:  In 
a  high  tank,  filled  to  one-half  with  strong  solution  of  chlor- 
ide of  magnesia,  sufficient  milk  of  lime  is  added.  The  lime 
produces  a  jelly-like  precipitate  of  magnesia  and  leaves  in 
solution  chloride  of  lime.  When  the  magnesia  has  well 
settled  the  solution  of  chloride  of  lime  is  drawn  off  by  sy- 
phon and  let  to  waste.  The  magnesia  is  then  washed  two 
or  three  times  with  clean  water;  it  is  then  ready  for  use 
and  is  added  to  the  bleach-liquid  in  small  quantities  as  re- 
quired. For  the  preparing  of  the  milk  of  lime  another 
tank  with  wash  drum  (the  latter  covered  with  very  fine 
metallic  cloth)  is  required.  The  wash  drum  draws  out  the 
milk  of  lime  and  leaves  sand  and  other  impurities  in  the 
tank. 

In  a  Swedish  cellstuff  factory,  during  several  years' 
bleaching  according  to  Hermite's  method,  for  each  100  Kgr 
cellstuff  11  Kgr  tale  are  decomposed  and  it  is  claimed  that 
bleaching  with  this  method,  although  twice  as  much  power 
is  required  than  stated  by  Hermite,  is  still  much  cheaper 
than  with  chloride^  of  lime. 

In  factories  where  the  wood  intended  for  boiling  is  cut 
by-  a  chip  machine  and  where  consequently  the  pieces  after 
the  boiling,  though  they  should  partially  be  left  hard,  are 
never  large,  and  where  besides  not  much  value  is  placed  on 
the  production  of  best  quality,  the  work  in  the  stampers 
and  in  the  wash  troughs  is  saved  by  crushing  the  stuff  dis- 
charged from  the  digester  directly  by  a  large  mill.  From 
there  the  stuff  is  let  into  a  basin,  diluted  with  water  and 


THE    MANUFACTURE    OP    CELLULOSE.  191 

directly  or  by  means  of  a  pump  conducted  to  the  Hollander. 
Here  it  is  beaten  for  some  time,  but  not  ground,  and  yet 
receives  an  addition  of  dilute  muriatic  acid,  whereby  the 
whiteness  of  the  stuff  is  raised,  afterwards  going  to  the  wet 
machine  for  finishing.  Because  in  this  method  the  knots 
are  not  all  removed  only  a  second  quality  stuff  is  naturally 
obtained. 

In  order  to  utilize  as  much  as  possible  the  knots  and  the 
stuff  adhering  to  them,  some  factories  use  still  another 
mill,  which  works  up  all  waste  and  crushes  also  the  knots,, 
at  least  into  small  pieces.  This  milled  stuff,  which  is  left 
possibly  dry,  is  scooped  into  a  quickly  rotating  sieve  drum 
of  inclined  position  which  sifts  the  stuff  which  can  be  made 
use  of  while  all  larger,  hard  pieces  come  out  at  the  lower 
end.  The  stuff  obtained  is  naturally  very  poor,  but  for 
sundry  purposes,  ordinary  paste-boards,  etc.,  it  still  finds 
employment. 

In  connection  with  the  fibring  arrangement  in  use  until 
recently  and  previously  described,  C.  Kleine  and  Ernest 
Kirchner  have  patented  a  method  in  which  a  rapidly  rotat- 
ing, so-called  twirler  is  connected  with  an  improved  ma- 
chine. The  description  reads  as  follows:  According  to  the 
present  invention  the  boiled  stuffs,  superficially  washed  in 
the  digester  or  in  special  leach  troughs,  are  drained  off, 
dan^),  or  by  adding  of  water  in  a  moderately  wet  condition, 
are  fed  through  funnel  T  (fig.  105)  and  by  the  worm  B  to  a 
twirl,  increasing  towards  the  back,  making  about  300  revo- 
lutions. The  twirl  revolves  in  an  entirely  closed  box  of 
quadratic  cross  section  with  blunted  corners  below  widen- 
ing towards  the  back  like  the  twirl.  The  damp  or  moder- 
ately wet  stuff,  regularly  fed  through  T  and  by  B,  in  so  far 
as  it  is  entirely  boiled  soft,  is  now  by  the  arms  of  the  twirl 
beaten  into  flakes  or  stiff  paste,  while  insufficiently  boiled 
or  hard  particles  are  completely  separated  from  good 
fibres,  but  otherwise  left  whole.  The  screw-like  arrange- 
ment of  the  arms  and  the  widening  of  the  box  towards  the 
back  effect  a  gradual  moving  of  the  stuff  to  the  opening 
provided  at  the  widest  part  of  the  box,  where  the  good 
stuff,  together  with  the  impurities  leaves  the  twirl,  as 
shown  in  the  illustration,  to  reach  through  a  drop-pipe  or 
a  special  transporting  arrangement  the  wash  and  cleaning 
arrangement.  Here  the  damp,  flaky,  or  thick  and  pasty  stuff 
is  diluted  by  plenty  of  water  from  the  upper  sprinklers  E 


192  THE    MANUFACTURE    OF    CELLULOSE. 

and  further  divided  by  a  mill-work  arrangement  C,  where- 
by the  large  impurities  are  left  whole.  The  latter  settle 
to  the  bottom  in  the  deep  troughs  by  the  water  entering 
from  the  lower  sprinklers  E,  i.  e.,  by  hydrostatic  pressure, 
they  are  freed  from  any  adhering  good  fibres  and  then  re- 
moved to  side  tanks  by  mechanism  H,  similar  to  chain- 
pumps.  Floating,  light  impurities  are  retained  by  wire 
nets  at  D;  heavy  particles,,  carried  along,  perhaps  by  the 
current  and  motion  of  the  liquid,  settle  again  in  the 
troughs  F  and  H,  rinsed  by  water  further  entering  from 
below,  from  where  they  are  removed  in  the  same  manner. 
The  now  very  wet  stuff  passes  a  sand  fang  K,  of  known 
construction;  by  one  or  several  wash  drums  L,  which  are 
arranged  directly  in  cavities  of  the  trough,  they  are  ener- 
getically washed  and  thickened.  The  thick  stuff  is  now 
completely  beaten  or  disssolved  in  single  fibres  by  a  mod- 
erately quick  rotating  rake-roller  M  with  base-rake. 

After  leaving  back  of  the  rake-roller  the  stuff  is  again 
much  diluted  by  a  sprinkler,  passes  again  a  sand  fang  K2 
and  several  troughs  N,  where  through  the  sprinklers  G,  ar- 
ranged below  water,  enters  again.  Thus  the  heavy  parts 
yet  contained  settle  in  the  troughs  N,  against  the  hydro- 
static pressure,  while  the  good  fibres  flow  on.  The  latter 
again  pass  a  sandfang,  are  a  second  time  washed  energetic- 
ally by  one  or  several  wash  drums  0  and  finally  reach  the 
stuff  press,  the  setting  boxes  or  the  bleach  hollander. 

Because  the  splinters,  as  undissolved  fibre  bundles,  as  a 
rule  are  rather  wide,  but  very  thin,  they  pass  easily  through 
all  these  processes  and  through  the  fine  slits  of  the  knot- 
fangers,  it  is  therefore  recommended  to  pass  the  stuff 
through  a  refiner,  the  semi-circular  slits  of  which  are  cut 
1  centimeter  deep.  The  refiner  entirely  dissolves  the 
splinters  and  if  managed  rightly  makes  the  fibres  uniform, 
without  injuring  them.  When  the  stuff  is  refined  and  thus 
free  of  splinters,  it  is  very  easily  bleached  and  can  be  used 
for  the  best  papers.  The  bleaching  of  sulphite  stuff  costs 
then  n-ot  more  than  2  to  3  marks  per  100  kilo. 

As  by  the  best  executed  washing  of  the  cellstuff,  the 
brown  digested  solution,  soaked  inside  the  single  fibres, 
can  be  removed  but  with  difficulty,  it  is  advisable  to  throw 
the  stuff  out  after  washing  by  a  centrifuge.  By  this  pro- 
cedure the  last  traces  of  leach  are  removed  and  the  stuff  is 
more  than  otherwise  susceptible  to  bleaching. 


THE    MANUFACTURE    OF    CELLULOSE. 


193 


194  THE    MANUFACTURE    OF    CELLULOSE. 

In  poorly  boiled  cellstuff  and  especially  waste,  according  to 
Mitscherlich,  pieces  often  occur  which  are  not  sufficiently 
boiled,  which  still  contain  much  resin  and  which  work  badly 
in  mill,  hollander  and  paper  machine.  It  has  been  recom- 
mended to  boil  these  pieces  with  1  1-2  per  cent,  of  the  dry 
weight,^  with  soda  in  the  form  of  balls  for  two  or  three 
hours  under  1  to  1  1-2  atmospheres  pressure,  whereby  the 
resin  is  dissolved;  also  when  milling  such  bad  pieces,  1  1-2 
to  2  liter  of  soda  and  3  liters  of  petroleum  is  added  to  100 
Kg  dry  stuff.  The  mass  must  then  be  washed  out  in  the 
wash  hollander  adding  1  to  1  1-2  liter  of  muriatic  acid  per 
100  Kg  stuff.  Instead  of  the  digester  a  large  barrel  with 
stirrer  may  be  used,  the  contents  of  which  can  be  boiled  for 
two  to  three  hours. 

According  to  a  method  of  Edward  Partington,  recently 
patented  in  England,  the  tar-like  traces  of  resin  often 
strongly  adhering  to  the  sulphite  stuff  may  be  removed  by 
paraffin  oil  or  any  other  carbon-hydrogen  combination 
which  is  added  to  the  stuff  in  the  wash  hollander.  For 
1,000  Kg  dry  stuff  Partington  recommended  7  to  9  liters  of 
ordinary  paraffin  oil  of  0.8-0.85  specific  gravity,  the  point 
of  inflammability  lays  between  17  and  490C. 

VI.  OFFENSIVE  WASTE-WATER  AND  ITS  PURI- 
FICATION, CONTAMINATION  OF  THE  AIR,  PRE- 
CAUTIONARY MEASURES,  STATUTES  OF  THE 
LAW. 

More  than  by  the  difficulties  of  the  very  manufacture  of 
cellulose,  more  than  by  the  injurious  influence  of  the  sul- 
phurous acid  on  all  iron  parts  and  on  the  durability  of  the 
digesters,  more  than  by  the  damage  done  to  the  vegetation 
of  the  neighboring  lands  by  the  gaseous  sulphurous  acid  es- 
caping from  the  towers,  more,  much  more  trouble  is  caused 
to  the  manufacturer  by  the  offensive  waste  waters,  where 
the  factory  is  not  favorably  situated  to  get  rid  of  them 
conveniently  amd  possibly  unnoticed.  The  amount  of  the 
waste  leaches  and  wash  waters  is  so  large,  and  the  quantity 
of  sulphurous  acid  still  contained  therein  so  considerable, 
besides  the  color  so  intense  and  the  smell  so  disagreeable, 
that  a  large  river  would  be  required  to  let  all  this  waste  go 
directly  into.  But  even  then  it  would  scarcely  go  without 
complaints,  suits  and  damages,  as  the  fishes  especially  are 


THE    MANUFACTURE    OP    CELLULOSE.  195 

sensitive  to  the  least  traces  of  sulphurous  acid  and  easily 
become  extinct.  Therefore,  when  planning  new  cellulose 
factories,  it  must  be  considered  essential  that  facilities  for 
letting  off  the  waste  waters  exist,  either  by  suitable  quality 
of  the  soil  or  by  large  water  currents  of  velocity,  and  the 
inlet  of  the  waste  water  must  not  take  place  close  above  a 
city,  but  below,  as  otherwise  the  molestations  would  never 
cease. 

For  a  boiler  according  to  Mitscherlich,  taken  for  a  basis, 
every  four  days  and  a  half  there  must  be  disposed  of  60 
cubic  meters  of  leach,  just  as  much  or  more  rinsing  water 
and  the  still  larger  quantity  of  wash  water.  The  off-leach 
is  boiling  hot  when  discharged  .and  the  running  water  also 
goes  off  quite  warm.  According  to  an  analysis  one  liter  of 
leach  contained:  Sulphurous  acid,  3.86  grammes;  sul- 
phuric acid,  7.33  grammes;  chlorine,  0.29  grammes.  The 
residue  dried  at  110°  C  weighed  109  grammes.  After  cal- 
cination there  remained  a  residue  of  19  grammes,  contain- 
ing: Iron  oxyde,  0.02  grammes;  lime,  10.30  grammes; 
magnesia,  0.30  grammes;  potash,  0.28  grammes;  soda,  0.10 
grammes;  a  total  of  11  grammes.  There  were  consequent- 
ly contained  in  one  liter  of  leach:  90  grammes  organic 
constituents,  in  one  cubic  meter  therefore,  90  kilo;  and  in 
60  cubic  meters  or  one  digester  charge,  the  collossal 
amount  of  5,400  kilos.  This  result  would  have  caused  sur- 
prise if  the  author  had  not  himself  ascertained  by  many  ex- 
periments that  for  100  kilos  of  finished  cellulose  291  kilos 
of  absolutely  dry  wood  are  required.  Almost  two-thirds 
are  consequently  lost,  and  these  are  made  up  by  the  knots, 
loss  of  fibre  in  manufacturing  and  the  incrusting  constitu- 
ents, which  reappear  in  the  leach.  Such  an  enormous 
amount  of  organic  constituents,  which  color  the  leach  quite 
dark  brown,  must  certainly,  even  without  considering  the 
presence  of  sulphurous  and  sulphuric  acid,  cause  a  strong 
contamination  of  the  water  currents  and  must  also  in  short 
time  penetrate  the  soil  of  the  environment  of  a  cellulose 
factory,  if,  as  is  done  as  a  rule,  the  leach  is  let  off  into  a 
so-called  leach  pond.  In  consequence  of  the  standing  still 
in  the  soil,  the  leach  will  then  soon  grow  rotten  and,  where 
perchance  appearing,  gives  out  a  sickly  smell.  By  this  pen- 
etrating through  the  soiland  all  joints  of  mason  work,  etc., 
it  is  then  quite  obvious  that  all  wells,  nearby  at  least, 
which  are  either  for  domestic  use,  o<r  furnish  the  water  for 


196  THE    MANUFACTURE    OF    CELLULOSE. 

manufacturing,  are  easily  ruined,  and  that  therefore  all 
possible  protective  means  must  be  provided  in  order  to  ef- 
fect absolute  isolation.  It  is  best  to  take  care,  when  plan- 
ning a' factory,  or  better  still  when  buying  and  selecting 
the  site  that  the  field,  if  not  immediately  situated  on  a 
large  river,  be  somewhat  hilly,  so  that  at  least  the  neces- 
sary water  for  manufacturing  can  be  taken  from  the  high- 
er lying  part,  while  the  wastes  should  be  let  off  or  sunk  as 
far  as  possible  from  the  factory.  No  matter  how  large  the 
river,  the  leach  must  not  be  run  off  at  once,  but,  as  the  dis- 
charging of  the  digesters  is  repeated  at  certain  intervals, 
the  regularly  renewed  quantity  must  be  led  off  in  a  small 
current,  or  during  the  night,  which  is  best  done  by  means 
of  a  gate  regulated  by  a  float;  besides,  however,  the 
waste  being  composed  of  three  parts,  the  digester  leach,  the 
rinsing  water  and  the  washings,  the  cooling  off  of  the  first 
two  must  be  effected  before.  Therefore  large  cemented 
basins  must  be  built  or  deep  pools  have  to  be  dug  and 
the  leach  and  washings  be  let  in  there.  Both  wastes  may 
also  be  collected  separately.  But  because  these  steaming 
wastes  still  contain  much  sulphurous  acid,  which,  if  freely 
streaming  into  the  air,  would  not  only  contaminate  the  sur- 
rounding atmosphere,  but  would  also  injure  the  vegetation 
of  the  neighborhood,  the  pools  must  be  well  covered,  and 
this  is  best  done  by  beams,  laid  over  with  bark  and  a  layer 
of  bark  chips,  which  again  are  covered  witL  earth.  This 
best  keeps  tight  and  can  be  easily  kept  in  repair. 

As  for  the  washings  which  contain  traces  of  sulphurous 
acid.,  it  is  generally  sufficient  to  conduct  it  away,  as  far  as 
possible,  through  several  basins,  which  by  dividing  walls 
are  separated  into  several  compartments.  Then  the  fine 
cellulose  particles  carried  along,  which  perhaps  nave  passed 
a  large  stuff  fang  which  the  washings  must  first  pass  shall 
next  settle.  The  stuff  fangs  may  be  rotating,  or  large  flat 
boxes  covered  with  fine  wire  netting.  It  is  well  to  set  into 
the  first  compartments  bundles  of  brushwood,  which  easily 
retain  the  cellulose  fibres  and  in  a  following  compartment 
to  let  the  water  through  a  layer  of  limestone,  mixed  with 
pieces  of  manganese,  whereby  sufficient  neutralization 
takes  place. 

But  if,  however,  the  water  current  at  which  the  cellulose 
factory  is  situated  is  insignificant  the  discharge  therein  of 
all  wastes  will  cause  such  contamination  that  complaints 


THE    MANUFACTURE    OP    CELLULOSE.  197 

will  never  cease  and  the  stepping  in  of  the  authorities 
would  necessarily  ensue.  Unfortunately  it  is  very  difficult 
to  render  harmless  the  sulphurous  acid.  The  different  ex- 
periments of  chemicals  and  also  all  present  methods  of  fil- 
teration,  which  with  the  dirty  waste  of  other  factories  were 
yielding  good  results  were  of  no  success  with  the  digester 
leach,  as  the  disagreeable  brown  color  could  not  be  got  rid 
of.  Where  therefore  direct  off-let  into  the  river  is  not  per- 
mitted., and  sinking  through  sandy  soil  is  not  sufficient, 
nothing  else  is  left  to  do  but  to  dig  several  deep  shafts 
down  to  the  ground  water  and  to  let  into  these  the  cooled 
leaches  and  eventually  the  washings.  This  can  only  be 
done  when  the  factory  is  situated  quite  isolated  and  human 
dwellings  and  wells  are  far  distant  in  the  direction  of  the 
descending  ground  water.  But  also  in  this  case  neutraliza- 
tion must  be  cared  for.  A  method  of  chemist  Leisenberg 
in  Halle  accepted  by  the  government  authorities  and  tried 
for  some  years,  in  cases  where  the  leaches  and  rinsing  are  to 
be  let  through  shafts  to  the  ground  water  and  the  wash 
waters  into  the  creek  is  as  follows:  Inside  the  factory,  best 
in  the  washroom,  are  put  up  as  high  as  possible  three  iron 
or  wooden  tanks,  which  all  have  water  supply  pipes,  can  be 
heated  by  steam  and  have  stirring  arrangement.  The  latter 
can  also  be  susbtituted  by  a  steam  injector,  as  furnished  by 
Koerting  in  Hanover,  which  permit  forcible  stirring  of  the 
liquid  in  the  tanks.  In  the  largest  of  tanks,  of  about  four 
cubic  meters,  milk  of  lime  is  prepared;  in  the  second  fer- 
rite  and  in  the  third  aluminate  is  dissolved.  All  three  liq^ 
uids  are  steadily  kept  stirred  up  by  the  steam  injector  or 
other  stirring  arangements.  A  pipe  about  50  mm  wide, 
which  can  be  closed  by  a  cock,  leads  from  the  lime  tank  to 
the  point  where  the  waste  enters  the  above  described  waste 
pool,  so  that  the  stream  of  lime  milk,  uniformly  running 
off,  regulated  by  the  cock  can  mix  as  thoroughly  as  possible 
with  the  wastes.  The  outlet  pipes  of  the  two  other  tanks 
discharge  cat  a  somewhat  distant  point  of  the  pond  and  in 
a  continuous  weak  current  a:dd  the  two  other  solutions  to 
the  waste  already  neutralized  by  the  milk  of  lime.  This 
method  requires  that  the  waste  flow  a  distance  of  100 
meters  or  more,  that  it  flows  through  one  or  more  deep 
pools,  where  the  current  is  so  low  that  the  lime  can  practi- 
cally settle  in  there  before  the  purified  wash  water  can  en- 
ter the  river.  It  has  been  found  that  this  method  frees  the 


198  THE    MANUFACTURE    OP    CELLULOSE. 

wash  water  of  almost  every  injurious  effect,  as  it  does  not 
become  rotten  or  foul  even  standing  for  weeks.  At  the 
same  time  the  color  also  becomes  somewhat  lighter.  The 
same  manipulation  is  employed  in  discharging  the  leach 
into  the  leach  pond,  but  as  this  discharging  is  only  done  at 
greater  intervals  one  large  tank  suffices  there  in  which  suc- 
cessively the  lime,  ferrite,  and  aluminate  are  dissolved  and 
from  there  are  mixed  with  discharging  leach  and  the  rins- 
ings. 

In  cases  where  a  sinking  of  the  leach  or  dropping  to  the 
ground  water  is  not  possible  or  permitted  by  the  authori- 
ties evaporation  is  the  only  remedy.  The  author  has  con- 
sequently tried  this  experiment  in  large  vessels  and  by  add- 
ing sulphuric  acid  has  quickened  the  expelling  of  the  sul- 
phurous acid.  H-e  obtained  a  thick,  syrup-like  mass  which 
after  cooling  became  stone  hard  and  could  be  broken.  For 
practice  on  a  large  scale  the  evaporating  tower  of  E. 
Schneider,  as  represented  in  fig.  20,  would  best  suit  for  the 
purpose  of  evaporation.  But  unfortunately  the  plant  is  too 
expensive,  as  the  product  of  evaporation  cannot  be  used 
with  profit,  as  in  the  regeneration  of  the  soda.  The  resi- 
dues of  evaporation  do  not  even  have  a  higher  fertilizing 
value.  These  residues  of  evaporation  have  been  recom- 
mended as  feed  stuff  for  stock,  used  either  alone  or  mixed 
with  other  feed  stuff,  but  the  author  has  not  learned  that 
experiments  have  led  to  any  practical  results. 

Dr.  Frank,  at  the  conclusion  of  a  lecture  already  men- 
tioned, is  of  the  opinion  that  the  feed  value  of  the  evapor- 
ated, or. at  least  concentrated  leach  is  not  small,  as  for  in- 
stance 16-18  per  cent,  of'  sugar  are  contained  therein;  but 
there  is  no  way  yet  to  utilize  the  leach  fitly,  besides  the 
transportation  O'f  the  leach  would  be  too  expensive  and  the 
evaporation  so  much  more  costly.  Nothing  else  is  left  to 
do  at  present  but,  according  to  Frank's  method,  to  remove 
as  much  as  possible  the  sulphurous  acid  and  eventually, 
where  it  can  be  done,  to  use  the  purified  leach  for  the  ir- 
rigation of  meadows  and  fields,  whereby  at  the  same  time 
the  difficulty  existing  with  many  factories  of  getting  rid  of 
the  leach  would  be  removed  in  the  most  simple  manner. 
The  carbonhydrates,  sugar,  etc.,  which  in  comparison  with 
their  high  food  value  have  but  small  fertilizing  value, 
thereby  yield  little,  but  the  mineral  constituents  of  the 


THE    MANUFACTURE    OF    CE-LLULOtSE.  199 

wood,  dissolved  in  the  leach,  directly  benefit  the  vegetable 
growth. 

One  cubic  meter  of  pine  wood  (quite  dry)  for  instance 
weighs  about  450  kilometer  and  furnishes  4  to  5  kilos  of 
clean  ashes,  corresponding  to  about  20  to  25  kilos  ordinary 
impure  wood  ashes;  consequently  to  every  one  who  is 
acquainted  with  the  utmost  favorable  yield  of  wood  ash 
fertilizing  for  feed  crops  and  especially  for  acid  meadows, 
the  advantage  of  rational  irrigation  will  be  clear.  The  re- 
peatedly mentioned  Frank  method  for  purification  of  the 
leach,  which  is  combined  with  the  recovery  of  the  sul- 
phuric acid,  consists,  according  to  his  own  statements,  of 
the  following:  The  sulphurous  acid  brought  into  the  di- 
gester with  the  sulphite  leach  is  only  in  a  small  part  con- 
sumed and  chemically  changed  in  the  process  .of  cellulose 
making,  while  the  larger  part,  about  70  per  cent.,  is  sep- 
arated in  the  form  of  monosulphite,  part  of  it  escaping  in 
gaseous  form,  which  part  of  it  together  with  the  leach  in 
which  it  is  dissolved,  is  carried  to  the  water  currents.  As 
then  the  'sulphurous  acid  in  gaseous  form  as  well  as  that 
conducted  away  with  the  leach,  can  become  very  trouble- 
some to  the  neighborhood  of  the  factories  and  injures  not 
only  man,  but  also  plants  and  animals.  By  it  manifold 
and  sometimes  quite  trying  disadvantages  have  been 
caused  to  the  management.  Mitscherlich  has  endeavored 
to  do  away  with  the  inconvenience  caused  by  escaping  of 
the  sulphurous  acid  with  the  vapors,  by  conducting  them 
into  the  towers.  Owing,  however,  to  the  great  rapidity 
with  which  the  vapors  enter  their  absorption  in  the  towers 
is  insufficient,  especially  during  the  hot  season,  and  the 
same  can  be  said  of  the  condensation  of  the  vapors,  which 
is  employed  by  factories  not  equipped  with  towers.  In  re- 
gard to  the  leaches,  which,  because  of  their  high  amount 
of  organic  substances  are  very  troublesome  in  smaller  wa- 
ter currents,  there  has  not  yet  been  found  a  practically 
useful  method  to  free  it  from  its  amount  of  sulphurous 
acid  and  other  injurious  substances.  The  evaporation  of 
the  leaches,  taken  up  by  several  factories,  has  proved  to  be 
a  very  costly  make-shift  on  account  of  the  rapid  destruc- 
tion of  the  evaporating  apparatus,,  the  enormous  consump- 
tion of  coal  and  the  absolute  worthlessness  of  the  residues 
of  evaporation  as  fuel,  the  more  as  with  the  very  evapora- 
tion the  sulphurous  acid  is  carried  along  into  the  air. 


200  THE    MANUFACTURE    OP    CELLULOSE. 

In  his  method  Dr.  Frank  endeavors  to  remove  only  those 
constituents  of  the  leach  and  vapors  which  are  proven  to 
act  injuriously.  As  such,  besides  the  sulphurous  acid  and 
its  combinations  in  solution  he  names  the  aldchyds  con- 
tained in  the  leaches  and  finally  the  dissolved  resin  and 
tar-like  substances,  which  in  later  separating  becomes  in- 
jurious to  the  gill  breathers,  as  to  the  plants  by  excluding 
the  air.  As  Dr.  Frank  has  proved  in  an  expert  report  the 
other  constituents  of  the  leaches,  mostly  sugar  and  am- 
gloides,  also  the  mineral  constituents  of  the  woods,  are  not 
only  entirely  harmless  and  well  suited  for  the  nurishing  of 
animals  and  plants,  but  also,  as  far  as  they  are  of  organic 
nature,  rapidly  and  completely  removed,  even  in  quite 
small  water  currents  by  oxydization. 

However,  in  order  not  to  make  the  purification  of  the 
leaches  too  'expensive  Dr.  Frank  combines  this  method  with 
the  recovery  of  the  sulphurous  acid  which,  together  with 
resins,  dye  stuffs  and  nitrogenous  constituents  he  precipi- 
tates in  the  form  of  the  almost  insoluble  mono-sulphate  of 
lime.  Then  the  liquid  freed  from  its  injurious  constitu- 
ents is  submitted  to  a  further  chemical  treatment  with  air 
and  carbonic  acid,  whereby  besides  the  oxydation  of  the 
aldchyds,,  also  the  small  amount  of  monosulphite  in  solu- 
tion is  transformed  into  the  entirely  harmless  sulphite  of 
lime  (gyps). 

The  precipitate  of  sulphite  of  lime,  as  obtained  is  very 
impure.  After  settling,  according  to  Dr.  Frank's  patented 
method,  it  is  freed  from  the  organic  substances  and  then 
.yields  a  perfectly  pure  sulphite  of  lime,  which  stirred  up 
with  water  and  charged  to  Frank's  leaching  apparatus  is 
worked  into  a  leach  perfectly  equal  to  a  fresh  sulphite  solu- 
tion by  simply  treating  with  sulphurous  acid. 

As  a  minimum  saving,  obtained  by  this  method  of  re- 
covery, Dr.  Frank  guarantees  33  per  cent,  of  that  qauntity 
of  sulphur  which  was  necessary  for  the  sulphite  solution 
originally  charged  to  the  digester,  so  that,  when  17  kilos 
of  sulphur  were  necessary  per  cubic  meter  of  leach  without 
recovery,  with  his  method  of  recovery  this  consumption  is 
reduced  to  two-thirds  or  about  11  kilos;  thus  bringing  the 
total  cost,  per  cubic  meter  sulphite  leach  down  to  33  per 
cent. 

However,  as  the  quantity  of  sulphurous  acid  left  un- 
changed in  the  digesting  process,  theoretically  estimated, 


THE    MANUFACTURE    OP    CELLULOSE.  201 

amounts  to  about  70  per  cent,,,  with  careful  management 
of  the  recovery  it  can  be  expected  to  recover  from  the  sul- 
phite leaches  up  to  about  50  per  cent,  of  the  sulphurous 
acid  and  thus  to  reduce  the  supply  of  sulphur  material  one- 
Jialf. 

The  installation  of  Frank's  method  for  the  purification 
and  recovery  of  the  leaches,  in  consequence  of  the  expert 
opinion  of  the  reputed  chemists,  Professor  Dr.  Medicus  and 
Professor  Dr.  Engler  has  been  officially  ordered  for  the 
cellulose  factory  in  Aschaifenburg,  and  on  account  of  the 
entirely  satisfactory  results  obtained  the  protests  and  com- 
plaints raised  against  the  working  of  the  factory  were  non- 
suited in  all  instances.  The  factory  in  Aschaffenburg  gives 
the*  daily  expense  of  the  method  as  12  marks,  the  value  of 
the  recovered  sulphur  material;  as  35  marks,  the  recon- 
sumption  of  the  latter;  as  40  per  cent.,  so  that  besides  the 
removing  of  the  formerly  existing  difficulties  in  regard  to 
running  off  the  leaches  there  is  left  a  daily  surplus  of  23 
marks,  amortizating  within  a  short  time  the  cost  of  the 
plant.  According  to  the  statement  of  the  inventor,  there 
are  at  present  in  Germany,  Austria  and  Sweden  a  large 
number  of  factories  engaged  to  install  his  method  and  for 
the  new  cellstuff  plant  of  the  Munkedal,  Achtiebolag,  Ud- 
devalla,  Dr.  Frank  has  even  accepted  guarantee  for  the 
fish  stock  of  the  mill  creek,  separated  by  a  grate. 

Dr.  Frank's  method  for  the  purification  of  the  leach  and 
recovery  of  the  sulphurous  acid  thus  appear  to  be,  for  the 
cellstuff  factories  as  well  as  for  their  neighbors  an  equally 
benefitting  solution  of  the  perplexing  question. 

A  perfect  conclusion  of  the  wash  water  question  will, 
however,,  not  be  reached  until  the  utilization  of  the  carbo- 
hydrates, -so  liberally  contained  in  the  leaches,  for  feeding 
purposes.  The  composition  of  the  leaches,  freed  from  the 
sulphurous  acid  and  the  resins,  according  to  his  investiga- 
tions, comes  near  to  that  of  the  molasses  residues,  but 
again&t  the  latter  has  the  advantage  of  containing  more 
sugar  (up  to  18  per  cent  of  dry  substance)  and  less  salts, 
The  production  of  aniline,  contemplated  by  some,  as  well 
»a  its  employment  for  the  manufacture  of  alcohol,  acetic 
acid  and.  naptha,  if  paying,  at  all,  requires  a  complicated 
plant,  so  that  for  the  present  it  will  be  well  to  take  in  con- 
sideration only  its  agricultural  utilization,  as  feed  for  the 
ptock,  or  its  use  for  irrigating  ari  fertilizing  fields  and 


202  THE    jy^ANUFACTURE    OF    CELLULOSE. 

mep-lc/vvs.     The  possibility  of  preparing  substances  useful 
in  the  arts  from  the  material  is  still  left  open. 

The  agricultural  utilization  left  entirely  out  of  the  ques- 
tion the  method  is,  however,  practical  for  all  those  factor- 
ies which  for  the  present  have  difficulties  on  account  of 
running  off  the  leaches,  as  the  leaches  freed  from  their 
directly  injurious  constituents  and  also  of 
proteids  give  little  cause  for  processes  of 
fermentation  and  purification,  as  well  as  for  the 
formation  of  algae,  and  even  in  moderate  dilution 
in  small  flowing  waters  suffer  rapidly  a  complete  oxydation 
and  self-purification  which  is  prevented  or  much  retarded 
by  the  presence  of  sulphurous  acid.  Besides  the  unpurified 
leaches,  containing  about  0.6  to  0.75  per  cent,  of  sulphur- 
ous  acid,  according  to  the  experiments  of  Dr.  Weigelt-Ku- 
fach,  when  let  into  waters  used  for  fish  culture,  require  a 
dilution,  corresponding  to  about  1,500  times  its  own  vol- 
ume. For  a  digester  charge  of  60  cubic  meters,  in  order  to  • 
satisfy  these  demands,  90,000  cubic  meters  of  water  must 
therefore  be  used,  a  quantity  not  everywhere  attainable. 

In  addition  to  this  it  may  be  mentioned  that  the  unpur- 
ified wastes  certainly  favor  the  formation  of  algae  in  the 
river  bed,  and  that  especially  with  small  water  currents 
the  disadvantage  comes  so  much  more  to  light  as  a  direct 
contamination  by  cellulose  fibres  can  be  seen.  These  algae 
form  principally  during  the  cold  season*,  and  disappear  al- 
most entirely  in  summer.  If,  however,  once  present,  they 
can  scarcely  be  eliminated  even  if  the  supply  of  leach  ceas- 
es entirely.  The  author  has  observed  that  five  years  after 
the  closing  of  a  factory  the  algae  reappear  regularly  in  the 
bed  of  the  river  during  winter. 

In  the  soda  eellstuff  manufacture  the  waste  leaches  can 
also  be  used  for  the  preparation  of  stock  feed.  A  Mr. 
Voigt  has  taken  out  a  patent  for  this,  No.  33,235,  and  gives 
the  following  as  his  method:  The  incrusting  constituents 
of  the  straw  and  likewise  of  the  wood  (consisting  of  carbon- 
hydrates,  proteins,  etc.,)  received  by  the  animal  make  up 
the  nutritive  part  and  are  completely  assimilated  by  the  an- 
imal organism  and  transformed  into  flesh  and  fat.  The  in- 
ventor therefore  aims  to  recover  in  the  form  of  press-cakes 
these  very  important,  nutritious  products,  which  in  cellu- 
lose manufacture  by  means  of  soda  enter  into  the  alkaline 
leach.  After  the  process  of  digesting  is  finished  the  alka- 


THE    MANUFACTURE    OP    CELLULOSE. 


203 


line  liquid,  much  admixed  with  organic  matter,  is  heated 
with  sulphuric  acid  until  neutral,  whereby  under  formation 
of  sulphate  of  soda  (Glauber's  salts)  all  organic  matter  dis- 
solved in  the  alkaline  liquid  (with  the  exception  of  some 
coloring  matter)  separate  in  the  form  of  a  most  finely  di- 
vided precipitate.  This  precipitate  is  then  separated  from 
the  sodium-sulphate  solution  by  means  of  a  filter  press, 
then  once  more  washed  with  water  and  again  pressed  and 
so  dried  in  the  shape  of  cake  and  brought  into  trade.  The 
A 


Fig.  106. 

product  thus  obtained  is  of  a  pleasant  scent  and  taste,  re- 
sembling fresh  hay  and  is  readily  eaten  by  horses,  cows  and 
sheep.  On  account  of  its  fine  division,  as  well  as  of  its  nu- 
tritive constituents,  it  is  almost  entirely  assimilated  by 
the  animal  organisms,  and  may  take  a  conspicuous  place 
among  the  food  essences  now  existing  in  commerce. 

In  regard  to  the  so-called  mother  liquor  (sodium  sul- 
phate solution)  still  left  it  is  evaporated  in  an  evaporating 


204  THE    MANUFACTURE    OF    CELLULOSE. 

pan  to  crystalization,  and  as  crystal  Glauber  salts 
brought  into  commerce.  According  to  the  view  of  others 
the  food  obtained  by  Voigt's  method  is  not  a  food  essence 
in  the  economical  agricultural  sense  of  the  word,  as  it  does 
not  contain  proteins  (albuminates)  as  these  have  already 
been  decomposed  when  boiling  the  wood  with  the  caustic 
leach.  They  admit,  however,  that  the  food  is  useful. 

To  prevent  the  injurious  effect  of  the  leaches,  Alexan- 
der Kumpfmiller  and  E.  Schultgen  obtained  a  patent  (D. 
R.  P.  No.  81,338)  on  the  method  described  below: 

The  waste  leaches  coming  from  the  digesters,  from  the 
vessel  A,  Fig.  106,  continuously  flow  into  the  tower  B, 
which  is  filled  with  a  rack  of  stones  and  serves  to  warm  the 
waste  leach,  and  at  the  same  time  to  cool  off  the  roast- 
ing shells.  A  distributing  arrangement  causes  the  leaches 
to  drizzle  evenly  through  the  whole  cross  section  of  the 
tower ;  and  they  collect  in  the  receptacle  F.  At  the  foot  of  the 
tower  the  hot  roast  gases  from,  the  pyrites  oven  D  enter 
through  pipe  E  into  the  tower,  give  off  their  heat  to  the 
leaches  drizzling  down  and,  cooled,  leave  the  tower  through 
pipe  C,which  conducts  them  to  the  absorption  apparatuses. 

By  the  action  of  the  roast  gases  on  the  leaches  a  reaction 
takes  place  between  the  sulphuric  acid  contained  in  the 
former  and  the  sulphite  acid  contained  in  the  latter  ac- 
cording to  the  equation: 

SO  3  plus  Ca  SO3  plus  H2O  equals  Ca  SO4  plus  SO2  plus 
H20. 

Consequently  the  sulphurous  acid  combined  with  lime, 
contained  in  the  leaches,  is  liberated,  while  at  the  same 
time  the  roast  gases  are  freed  of  sulphuric  acid,  whereby 
the  formation  of  gyps  crusts  in  the  lower  parts  of  the  ab- 
sorption apparatus  is  avoided. 

From  the  foot  of  the  tower  the  hot  waste  leaches  are 
raised  through  pipe  G  into  a  vacuum  apparatus  H  and  as  a 
thickened  liquid  continuously  flows  through  pipe  K  into 
the  reservoir  J,  placed  about  10  meters  below. 

With  the  spray,  evolved  under  the  influence  of  the  vac- 
uum in  the  spray  condensor  L,  which  is  fed  with  lime  wa- . 
ter,  the  steam  vapors  are  condensed  and  the  sulphurous 
acid  is  absorbed.  The  water -of  condensation  therefore,  af- 
ter previous  cooling,  can  partially  again  be  used  for  feed 
water,  partially,  as  so-called  half  leach,  it  can  be  pumped 
to  the  absorption  towers. 


THE    MANUFACTURE    OP    CELLULOSE.  205 

Two.  spray  condensers  can  be  used;  in  this  case  the  one  L 
is  fed  with  water  for  the  condensation  of  the  steam  vapors, 
the  other  L,  with  lime  water,  to  bind  the  sulphurous  acid, 
so  that  the  sulphite  of  lime  formed  is  collected  in  reservoir 
III,  separately  from  the  water  of  condensation. 

The  ejector  N  serves  to  produce    the    vacuum,    when 
starting  the  plant;  it  can  also  be  employed  to  conduct  the 
sulphurous  acid  gas  from  escaping  from  the  first  condenser - 
immediately  into  the  pipe  C. 

A  new  patent  for  the  utilization  of  leaches  has  been  tak- 
en out  by  the  stock  company  Xylolyse  and  Dr.  Emil  Meyer 
in  Berlin  (D.  E.  P.  No.  45^951)  for  a  method  for  the  pro- 
duction of  liquid  products  of  distillation  from  cellstufi 
leaches.  It  reads  as  follows:  In  the  production  of  cellstuff 
from  wood  almost  one-half  of  the  weight  of  its  dry  sub- 
stance is  brought  in  solution  by  the  leaches.  By  supplying 
heat  by  means  of  steam  coils  the  waste  leach  from 
the  soda  process  can  be  condensed  down  to  35°  B. 
The  condensed1  leach  is  mixed  with  40  to 
55  parts  by  weight  with  charcoal,  and  then  formed 
in  uniform,  durable  and  transportable  pieces,  permitting 
further  drying  in  heating  chambers,  or  they  may  with  the 
original  amount  of  water  at  once  be  charged  into  red-hot 
retorts,  without  damaging  by  sudden  cooling  off  and  with- 
out losing  their  form  in  charring. 

The  distillation,  damping  and  cooling  of  the  residue 
charcoal,  the  collecting  of  the  tar,  the  gas  water  and  the 
gases  differ  in  no  wise  from  similar  known  processes.  Only 
the  product  of  distillation  itself  differs  from  that  of  the  or- 
dinary charring  of  wood  in  retorts,  in  so  far,  as  formic 
acid,  acetic  acid,  etc.,  do  not  appear,  but  only  methgl-al- 
cohol,  etc.,  and  diverse  amine  combinations  are  dissolved 
in  the  water  of  condensation;  also  a  tar  of  different  quality 
is  obtained  from  this  resulting  to  the  management  the  ad- 
vantage that  instead  of  copper  for  the  rondensors  iron  can 
be  used  and  in  rectification  of  the  gas  water  its  volatile, 
valuable  products  can  be  obtained  by  distilling  off  a  small 
quantity. 

If  the  acid  leaches  of  the  sulphite  process  are  intended 
to  be  worked  in  this  mannej  the  free  acid  must  first  be 
eliminated.  Further  because  the  lime  in  solution  in  ac- 
cumulating would  in  the  end  disqualify  the  coal  residue,  it 
is  to  be  recommended  to  precipitate  it  as  sulphate  by  add- 


206  THE    MANUFACTURE    OF    CELLULOSE. 

ing  gla-ubor  salts,  which  can  always  be  recovered. 

When  distilling  the  sulphite  leaches  and  also  the  alka- 
line leaches  of  the  so-called  sulphate  cellulose  containing  sul- 
phide of  sodium,  besides  the  aceton  and  the  methyl  alcohol, 
other  volatile,  sulphuric  cercaptanic  and  alkylthio-ear- 
bonic  combinations  are  formed  which  are  neither  com- 
pletely condensed  nor  are  they  made  harmless  when  burned 
with  the  resulting  gas,  with  which  they  are  mixed. 

Another  utilization,  or  rather  recovery  of  spent  sulphite 
leaches,  is  done  by  apparatuses  which  are  built  by  the  Gol- 
zern  Machine  Works. 

In  the  sulphite  stuff  manufacture  a  liberal  third  of  the 
sulphurous  acid  gets  lost,  about  one-sixth  is  retained  in  the 
leaches  and  runs  off  with  the  washings;  and  just  as  much 
escapes  with  off -vapors  into  the  atmosphere.  In  this  manner 
scarcely  two-thirds  of  the  sulphurous  acid  charged  to  the  di- 
gestor  are  utilized,  and  sometimes  still  less. 

To  remedy  this  disadvantage,  Director  Rudulf  Kron,  iu 
Golzern,  has  invented  a  simple-  plant  for  the  purpose  of  the 
recovery  of  sulphurous  acid  contained  in  waste  waters  and 
in  the  off-vapors.  The  practical  trial  also  yielded  a  saving 
of  sulphur  30  to  40  per  cent,  equal  to  a  price  reduction  of 
from  5  to  10  marks  per  ton  of  cellstuff.  At  the  same  time 
the  present  rather  general  contamination  of  the  atmos- 
phere and  of  the  factory  water  is  prevented. 

The  Papier  Zeitung  publishes  another  method  for  the 
purification  and  utilization  of  the  leaches,  resulting  from  the 
manufacture  of  sulphite  stuff,  by  Viggo  Beutner  Drewson. 
The  method  consists  in  the  treatment  of  the  spent  leaches 
with  caustic  lime,  if  possible  free  of  carbonic  acid,  at  higher 
temperature  and  with  the  application  of  pressure. 

If  the  leach  used  in  the  sulphite  stuff  manufacture,  which 
possesses  a  distinct  acid  character,  is  treated  with  caustic 
lime  at  ordinary  temperature,  it  combines  with  the  present 
sulphurous  acid  to  make  lime  monosulphite.  The  leach  liquid 
of  now-changed  condition  has  lost  the  capacity  to  hold  irs 
solution  part  of  the  organic  substances,  which  were  dissolved 
in  the  acid  solution,  and  they  are  precipitated,  together 
with  the  lime  monosulphite.  The  process  results  at  boiling 
temperature  in  the  same  manner  as  at  ordinary  tempera- 
ture. 

Quite  different,  however,  is  the  result  of  the  action  of  the 


THE    MANUFACTURE    OF    CELLULOSE.  207 

caustic  lime  on  the  sulphite  leach,  when  both  are  heated  to- 
gether to  higher  temperature  under  pressure  in  a  closed  ves- 
sel, because  then  the  lime  is  able  to  decompose  the  organic 
combinations  dissolved  in  the  spent  leach,  originating  from 
the  incrusting  substances  of  the  wood.  If,  then,  the  bottom 
sediment,  obtained  by  treating  the  spent  leach  with  caustic 
lime  at  about  6  atmospheres  pressure  and  treating  it  with 
muriatic  acid,  is  filtered  off,  considerable  quantities  of  sul- 
phurous acid  escapes,  while  at  the  same  time  a  bottom- 
sediment  of  organic  substances  insoluble  in  water  and  acid 
is  left  contaminated  with  sulphate  of  lime.  The  light  yellow 
leach,  filtered  off  from  the  original  bottom-sediment,  pro- 
duced by  the  caustic  lime,  when  evaporated,  leaves  but  a 
small  fraction  of  the  substances  contained  in  the  spent  leach, 
because  the  more  readily  decomposed  sulphur  substances  as 
well  as  the  principal  amount  of  the  organic,  so  called  incrust- 
ing substances,  are  precipitated.  Operating  with  this  process 
it  is  therefore  possible,  with  such  a  cheap  material,  as  given 
in  the  caustic  lime:  (1)  To  purify  the  spent  leaches,  and  to 
dispose  of  them  in  a  simple  and  harmless  manner;  and 
(2)  to  produce  substances  of  material  importance  to  the  arts. 
In  practice  the  present  method  is  carried  out  as  follows: 
After  the  finishing  of  the  digesting  process  the  spent 
leach  is  charged  under  pressure  into  a  closed  vessel,  provided 
with  a  stirrer,  in  which  is  contained  already  the  required 
amount  of  caustic  lime,  as  much  as  possible  rid  of  carbonic 
acid.  Because  of  the  immediate  neutralization  of  the  acid, 
this  vessel  may  be  of  iron.  As  soon  as  the  spent  leach  has 
all  been  blown  over  into  the  vessel,  steam  is  admitted,  the 
stirrer  is  set  in  motion,  and  the  temperature  is  maintained 
at  a  certain  height  corresponding  to  about  6  atmospheres, 
until  a  test  indicates  that  the  reaction  is  finished.  As  soon 
as  this  is  the  case  the  contents  of  the  vessel  are  filtered  by 
a  filter  press.  The  light  yellow  liquid  of  alkaline  reaction 
running  off  is,  when  necessary,  treated  with  carbonic  acid 
by  passing  over  it  the  products  of  combustion  from  a  chimney 
by  means  of  a  koerting  injector,  to  neutralise  the  alkalinity. 
The  filtered  off  bottom-sediment,  consisting  of  calcium- 
monosulphite,  calcium-sulphate  and  of  the  lime  combina- 
tions of  the  organic  substances  formed  from  the  incrusting 
substances  of  the  wood,  is  then  used  in  place  of  limestone  or 
limemilk  for  preparing  the  bisulphite  leach.  In  treating 


208  THE    MANUFACTURE    OF    CELLULOSE. 

with  sulphurous  acid  there  are  left  indissolved  principally 
the  organic  combinations  which  are  filtered  off  in  a  filter 
press,  while  the  filtrate  is  returned  for  use  in  boiling  wood  in 
the  manufacture  of  sulphite  cellstuff,  exactly  like  the  ordi- 
nary bisulphite  leach. 

In  this  manner  one-fourth  to  one-half  of  the  original 
-  amount  of  sulphur  is  recovered.  The  organic  substances,  se- 
cured by  this  method,  can  be  used  for  different  purposes. 

For  a  clear  illustration  of  the  correctness  of  the  above- 
mentioned  proposition  of  Dr.  Frank,  to  use  the  purified 
wastes  for  irrigation,  and  thus  at  the  same  time  causing  self- 
improvement  of  contaminated  river  water,  a  case  from  prac- 
tice may  serve.  It  is  about  the  contamination  of  a  small 
creek,  in  total  carrying  capacity  about  one  cubic  meter  of 
water  per  minute,  by  the  spent  liquors  of  a  sulphite  cellulose 
factory.  Dr.  Frank  had  been  appointed  expert  to  give  his 
opinion  whether  the  complaints  that  the  water  be  fit  neither 
for  domestic  purpose,  nor  for  the  irrigation  of  meadows, 
were  just,  and  whether  a  remedy  could  be  had.  It  is  now 
scientifically  proved  that  water  contaminated  with  organic 
matter  in  solution  in  long  contact  with  air,  especially  witn 
much  fall,  is  again  purified,  that  consequently  in  this  pro- 
cess the  oxygen  dissolved  in  water  proves  to  be  more  active, 
than  the  less  active  oxygen  of  the  air.  But  as  water  in  the 
presence  of  sulphurous  acid  cannot  contain  oxygen,  the  self- 
purification  of  water  mixed  with  larger  quantities  of  sulphite 
leach  would  be  but  insignificant.  Nevertheless,  even  in  this 
unfavorable  instance,  a  decrease  of  the  organic  matter  with 
simultaneous  oxidation  of  the  sulphurous  acid  to  sulphuric 
acid  can  be  proved.  The  following  analyses  serve  as  vouchers 
for  this: 

Sample  1.  The  creek  water,  when  entering  the  factory, 
contained  in  one  million  parts  a  total  residue  per  liter  of 
150  mg.;  of  this:  organic  matter  78,  lime  42,  sulphurous 
acid  0. 

Sample  2.  Mixture  of  leach  and  leach  wash-water,  when 
leaving  receptacle,  contained  in  one  million  parts  a  total 
residue  of  58,450  mg. ;  of  this:  organic  matter  42,200,  lime 
5,658,  sulphurous  acid  1,66$. 

Sample  3.  The  creek  water,  taken  5  kilometers  below  the 
factory,  contained  in  one  million  parts  a  total  residue  of 
1,600  mg. ;  of  this:  organic  matter  600,  lime  184,  sulphurous 
35. 


THE    MANUFACTURE    OP    CELLULOSE.  209 

A  further  effective  purification,  scarcely  worthy  of  con- 
sideration in  currents  with  abundant  water,  would  be  ob- 
tained in  this  case  by  employing  the  small  creek  for  irri- 
gation purposes,  because  the  soil,  by  its  absorbing  and  oxy- 
dizing  influence,  not  only  diminishes  the  organic  matter, 
but  also  the  amount  of  lime.  In  this  irrigation  also  the 
most  valuable  mineral  constituents  of  the  wood,  potash,  etc., 
would  do  good  service. 

To  test  the  behavior  of  purified  leaches  by  experiment,  part 
of  the  spent  leach  (Sample  2)  was  freed  from  sulphurous 
acid  and  resins,  according  to  Dr.  Frank's  method.  Although 
after  this  operation  the  liquid  appeared  somewhat  darker 
than  the  acid  leach,  after  diluting  with  thirty  times  its 
amount  of  water,  and  longer  contact  with  air,  it  proved  to 
contain  one-half  less  of  organic  matter  than  Sample  3,  and 
also  the  color  was  lighter,  after  adding  water.  But  much 
more  distinctly  did  the  success  of  the  purification  appear  by 
this,  that,  while  Sample  3  notwithstanding  its  high  amount 
of  sulphurous  acid,  inside  of  two  days  appeared  very  turbid; 
the  sample  made  of  purified  leach  with  equal  dilution  kept 
perfectly  clear  for.  8  to  10  days  under  the  same  conditions.  It 
was  still  less  difficult  to  prove  by  figures  and  by  experiments 
on  a  large  scale  that  the  recovery  of  the  sulphurous  acid  con- 
nected with  the  purification  of  the  spent  leaches,  besides 
covering  all  expense,  yielded  a  considerable  surplus. 

From  these  experiments  it  seems :  That  the  waste-waters 
in  question,  after  they  are  freed  from  sulphurous  acid  and 
resinous  particles,  do  not  in  any  manner  harm  the  vegeta- 
tion, but  are  especially  suited  for  the  irrigation  of  meadows 
and  fields,  because  they  contain  numerous  valuable  fertiliz- 
ing substances.  Also  that  the  purified  waste-waters  admitted 
to  the  river  are  not  injurious  to  fish  and  warm-blooded  ani- 
mals, and  are  useful  for  many  domestic  purposes,  as  num- 
berless spring  waters,  serving  to  supply  cities,  show  a  higher 
amount  of  lime  than  the  creek  water  of  Sample  3. 

Then,  although  larger  river  currents  are  at  the  disposi- 
tion of  most  cellulose  factories,  to  receive  their  wastes,  the 
extreme  case  here  cited  proves  that  only  the  directly  in- 
jurious constituents  need  to  be  removed  from  the  waste- 
waters  of  the  sulphite  leach,  while  for  the  removing  of  the 
organic  matter  in  solution,  sugar,  amyloids,  etc.,  in  them- 
selves quite  harmless,  the  energetic  self -purification  in  the 
river  can  be  counted  upon  with  confidence. 


210  THE    MANUFACTURE    OP    CELLULOSE. 

Some  instructions  by  the  government,  which  have  already 
proven  successful,  are  the  following: 

The  spent  leachs,  or  spent  leaches  and  washings  together, 
are  to  be  treated  with  caustic  lime,  so  that  they  are  ren- 
dered almost,  but  not  quite,  neutral.  The  last  remnant  of 
acid  is  to  be  removed  by  gradual  treatment  with  limestone, 
while  admitting  air. 

To  regulate  the  latter  process,  impenetrable  collecting 
ponds  are  to  be  built,  which  will  hold  fourteen  times  the 
amount  of  the  daily  produced  quantity  of  spent  leach  and 
from  which  it  can  be  run  off  at  the  upper  edge. 

Drawing  off  may  be  done  when  thorough  neutrality  of  the 
liquid  has  ensued,  but  only  into  water  currents,  which  cause 
a  dilution  five  hundred  times  the  off-run. 

Another  cause  for  the  contamination  of  the  water  in  cellu- 
lose factories  is  by  the  pyrites  residues  stored  away  in  heaps. 
During  heavy  rains  they  are  leached  out,  and  the  water 
running  ofl>  like  the  other  not  purified  waste-waters,  act? 
injuriously  and  must  therefore  be  conducted  off  in  such  a 
way  that,  together  with  the  other  waste-waters,  it  can  be 
purified  or  dropped.  The  residues  themselves  make  a  very 
good  material  for  roads ;  because  they  make  such  hard  roads 
and  do  not  permit  any  vegetation  to  come  out. 

When  the  pyrites  residues  are  heaped  up  near  a  river,  great 
damage  can  be  easily  done  when,  during  a  Hood,  the  residues 
are  carries  off  over  fields  and  meadows,  and  thus  great  sur- 
faces can  for  years  at  least  be  made  partially  sterile. 

In  the  neighborhood  of  cellulose  factories  complaints  are 
general  about  contamination  of  the  air.  With  the  sulphite 
cellulose  factories,  especially  if  no  residences  are  nearby,  the 
evil  is  not  so  very  bad,  as  the  annoying  smell  is  present  only 
when  the  necessary  care  is  not  taken. 

The  soda  cellulose  factories  have  greater  difficulties  to 
combat  in  this  respect.  When  discharging  the  digester,  and 
in  the  process  of  recovering  the  soda,  gases  escape  which  may 
be  compared  to  the  odor  of  foul  cabbage,  and  which  some- 
times appear  so  strongly  that  the  whole  country  for  a  great 
distance,  according  to  strength  and  direction  of  the  wind, 
is  made  to  suffer.  Notwithstanding  the  fact  that  the  gases 
frequently  evolved 'in  evaporating  the  leaches  are  conducted 
over  fires,  and  there  consumed,  the  extremely  suffocating 
smell  can  scarcely  be  avoided,  especially  as  some  manufac- 
turers are  not  able  even  to  tell  exactly  where  the  principal 
stench  really  comes  from. 


THE    MANUFACTURE    OP    CELLULOSE.  211 

Iii  consequence  of  the  undeniable  harm  done  the  neigh- 
borhood, in  many  countries  the  authorities  were  prompted 
to  proceed  against  the  cellulose  factories  in  regard  to  con- 
tamination of  the  atmosphere,  and  indeed  at  some  places 
this  was  done  in  such  a  manner  that  the  very  existence  of 
the  factories  was  jeopardized.  This  appeared  most  strik- 
ingly in  the  case  of  the  Koeslin  cellulose  factory,  situated 
1,500  meters  distant  from  the  city,  and  where  the  government 
on  account  of  the  suffocating  vapors  for  every  special  in- 
stance imposed  a  fine  (eventually  six  days'  imprisonment  of 
the  manager.)  In  several  instances  this  fine  was  also  col- 
lected, although  counter-suits  were  instituted,  lasting  for 
years,  and  although  everything  was  done  to  diminish  the 
nuisance  to  the  smallest  possible  measure. 

The  many  complaints  about  contamination  have  now 
caused  the  authorities  to  impose  severe  conditions  for  the 
management  of  cellulose  works.  For  example,  the  following 
for  a  soda  cellulose  plant: 

First — The  manufacturer  has  to  adhere  to  the  method  of 
manufacture  as  described  by  him  in  all  its  parts,  especially 
must  all  operations  of  digesting,  washing  and  evaporating 
be  conducted  in  perfectly  closed  systems. 

Second — All  parts  of  apparatuses  (new  and  old  digesters, 
blow-off  cylinders,  pipe-lines,  etc.),  in  which  are  contained 
liquids  heated  or  treated  under  pressure,  must  be  made  per- 
fectly tight.  At  the  least  untightness  noticeable  the  re- 
spective part  of  the  apparatus  is  at  once  to  be  cut  out  and 
repaired,  arid  not  to  be  put  in  use  again  until  answering  the 
test  described  by  law  (certificate  of  the  boiler  inspection.) 

Third — Inside  of  twenty-four  hours  not  more  than  eight 
charges  shall  be  emptied.  In  order  to  control  this  limit  of 
production  the  respective  book  of  changes  must  at  any 
time  be  accessible  to  the  representative  of  the  government. 

Fourth — The  conducting  of  the  leaches,  from  the  digesters 
as  well  as  from  the  blow-off  cylinders  to  the  end-leach  re- 
ceiver, and  from  there  to  the  closed  condensers,  must  all 
through  be  done  in  closed  pipes. 

Fifth — The  end-leach  receiver  itself  must  also  be  hermet- 
ically closed  against  the  outer  air;  and  the  place  for  the  air 
to  enter  when  blowing  off  the  leach  must  be  provided  with 
an  automatic  valve  opening  inside. 

Sixth — The  vapors  produced  in  the  digester  must  be  blown 
off  continuously  and  by  a  surface  condenser  with  water  cool- 


212  THE    MANUFACTURE    OF    CELLULOSE. 

ing  and  sufficiently  large  condensing  surface  must  be  con- 
ducted to  two  receptacles,  in  which  the  separation  of  con- 
densed oil  and  water  goes  on.  The  dimensions  of  these  re- 
ceptacles must  be  such  that  a  complete  separation  of  the  oil 
takes  place,  before  emptying.  This  oil  must  be  carried  off  in 
well-closed  vessels  and  provision  must  be  made  that  in  sepa- 
rating the  water  it  does  not  come  in  contact  with  the  outer 
air.  The  gases  not  condensed  in  the  coolers  must  be  con- 
ducted in  closed  pipes  to  a  fire,  and  there  be  entirely  con- 
sumed. From  the  reservoirs  the  water  left  after  removing 
the  condensed  oil  is  to  be  pumped  into  an  apparatus  in  which 
by  a  heating  coil  the  last  traces  of  the  volatile  oils  and  odors 
are  expelled,  and  also  burned  in  a  grate  fire. 

Seventh — The  vapors  leaving  the  second  condenser,  if  still 
containing  uncondensed  gases,  cannot  be  used  to  heat  the 
leach  mixture,  but  must  be  .condensed  by  themselves,  and 
the  uncondensable  part,  as  under  sixth,  must  be  burned  in  a 
grate  fire. 

Eighth — All  hitherto  mentioned  gas  conductors,  leading 
under  the  grate  fires,  must  end  in  the  form  of  a  spray  under 
the  middle  of  the  respective  fire  grates. 

Ninth — The  fire-wall,  inclosing  the  ante-room,  must  be 
constructed  in  such  manner  that  it  cannot  become  untight. 
If  untightness  should  show,  no  leach  shall  be  evaporated  in 
this  ante-room. 

Tenth — The  gases  from  the  ovens  before  entering  the 
chimney  must  be  made  to  pass  a  final  fire,  so  that  all  odors 
left  are  consumed.  If  the  ordinary  grate  fire  should  not 
fulfill  its  purpose  with  sufficient  completeness  it  is  to  be  re- 
placed by  a  regenerative  gas  fire  with  highly  heated  air. 

Eleventh — The  lyes  prepared  for  digesting  should  not  con- 
tain more  than  10  per  cent,  sulphide  of  sodium  of  the  amount 
of  soda  (caustic  soda  and  carbonate  of  soda  figured  on  the 
latter)  in  the  leach. 

Twelfth — The  observation  of  all  permit  conditions,  the 
maximum  amount  of  sodium  sulphide  of  the  leaches,  as  well 
as  the  question  of  retaining  and  consuming  of  the  odorous 
gases,  is  placed  under  chemical  and  technical  supervision. 

Thirteenth — The  wash-waters,  yielded  in  washing  out  the 
leaches  adhering  to  the  digested  wood  stuff  in  the  blow-off 
cylinder,  must,  before  being  admitted  to  the  river,  be  mixed 
with  the  spent  liquors  of  the  chlorine-bleach. 

The  changes  made  in  the  soda  factory  in  question  con- 


THE    MANUFACTURE    OP    CELLULOSE. 


213 


sist  of  the  following:  The  wood  is  not  boiled  to  a  finish 
with  the  same  leach,  but  the  leach  is  gradually  circulated 
in  the  digesters,  being  in  four  different  states,  so  that  finally 
the  stuff  comes  in  contact  with  pure  leach.  The  digesters  are 
no  longer  blown  out  into  the  open,  but  into  closed  vessels, 
and  there  thoroughly  washed  out. 

Thereby  less  but  more  concentrated  leaches  are  obtained 
for  the  calcining  process;  and,  further,  the  epening  of  the 
digesters,  filled  with  hot  stuff  which  was  part  of  the  cause 
of  the  complaint  of  the  neighborhood,  is  entirely  avoided. 
The  complete  combustion  of  the  gases  produced  in  calcining 
is  also  aimed  at  by  the  calcining  oven  containing  three 
equally  divided  fireplaces,  so  that  at  the  end  of  the  oven 
all  gases  must  again  pass  a  powerful  fire,  worked  with  .strong 
supply  of  air.  Of  the  products  of  combustion  of  this  pro- 


Fig.  107. 

cess  more  than  50  analyses  were  made  in  different  parts  of 
the  oven,  and  of  the  chimney  at  the  different  states  of  work, 
and  at  different  times,  because  it  has  been  apprehended  that 
hydrogen  sulphite  could  be  produced  by  the  dry  distillation  of 
sulphide  of  sodium  formed  from  the  sulphate  of  soda.  This 
presumation,  however,  has  not  been  confirmed;  sulphide  of 
hydrogen  was  not  formed  at  all  by  the  analyses,  or  in  such 
small  quantities  as  found  in  the  products  of  combustion  of 
every  larger  coal  fire.  It  could,  consequently,  not  be  settled 


214  THE    MANUFACTURE    OF    CELLULOSE. 

that  the  employment  of  sulphate  of  soda  with  the  arrange- 
ments made  would  cause  any  additional  inconveniences. 

The  arrangements  as  prescribed  for  rendering  harmless 
the  water  of  condensation  originating  from  blowing-off  the 
digester  are  illustrated  in  the  sketch  (Fig.  107)  and  for  its 
explanation  the  following  is  to  be  said:  After  the  vapors 
produced  when  blowing  off  the  over-pressure  of  the  digesters 
have  been  conducted  through  a  condenser,  the  waters  of 
condensation  and  the  uncondensed  vapors  are  alternately 
passed  through  the  pipes  a  a  by  means  of  valves  b  b  to  the 
closed  iron  reservoirs  A  A.  In  these  accumulates  the  water, 
while  the  uncondensed  vapors  are  through  the  pipes  i  i  con- 
ducted under  a  fire,  where  they  are  consumed  with  a  bluish 
flame. 

While  the  one  reservoir  A  is  filling  the  other  is  standing 
still  for  5  to  6  hours;  during  which  time  the  oily  substances 
separate  on  top.  The  latter  are  then  let  off  by  the  outlets 
c  c  c  provided  with  valves,  and  burned  in  a  fire.  The  liquids 
cleared  off  in  the  reservoirs,  which  always  contain  odorous 
substances,  are,  through  the  pipe  connections  d  d  and  e 
pumped  to  the  closed  iron  vessels  B  and  heated  by  the  steam 
coils  g  g.  The  last  traces  of  the  odorous  substances  are  here 
volatized  and  through  h  reach  a  fire,  where  they  are  also 
burned  up.  The  spent  water,  freed  from  its  odorous  sub- 
stances in  the  vessel  B,  after  it  has  gone  through  a  process 
of  precipitation  and  clarifying  with  caustic  lime,  is  let  off 
through  f  and  re-employed  in  the  factory. 

For  .the  sulphite  cellstuff  factories,  after  hearing  several 
experts,  more  severe  instructions  were  issued  by  some  au- 
thorities, for  which  the  following  points  may  serve  as  an 
example.  These  were  made  for  the  Aschaffenburg  paper  fac- 
tory previous  to  the  erection  of  a  sulphite  cellulose  plant : 

First — The  extensions  of  the  factory  plant  must  be  exe- 
cuted exactly  according  to  the  plans  submitted  and  under 
compliance  with  the  instructions  of  the  general  building 
regulations. 

Second — For  the  additional  steam  boiler  a  permit  of  the 
Bavarian  Association  for  steam  boiler  revision  must  be  de- 
posited in  regard  to  its  safety,  as  well  as  to  completeness  and 
tightness  of  its  armature  parts. 

Third — All  arrangements,  as  far  as  the  chemical  depart- 
ment is  concerned,  must  be  such  that  sulphurous  vapors  can- 
not escape.  Therefore  all  apparatuses,  absorption  and  di- 


THE    MANUFACTURE    OF    CELLULOSE.  215 

gesting  apparatuses  and  all  pipe-lines  must  always  be  main- 
tained in  condition  and  the  draft  in  the  sulphur  pans  is  to 
be  regulated  in  such  manner  that  sulphurous  acid  cannot 
escape. 

Fourth — The  digester-vapors  must  not  escape  into  the  open 
air  when  blowing  off  the  boiler,  but  must  be  conducted  par- 
tially through  pipe-lines  which  can  be  shut  off  partially  by 
putting  in  injectors;  they  have  to  be  conducted  into  freshly 
charged  digesters. 

Fifth — The  purification  and  carrying  off  of  the  waste - 
waters  must  be  done  separately  from  those  of  the  soda  cell 
stuff  factory.  The  diluted  spent  leaches,  before  admitting  to 
the  Aschaff,  must  be  submitted  to  Dr.  Frank's  method  of 
purification,  whereas  the  water  coming  from  the  rest  of  the 
plant,  especially  from  the  wash-hollander,  must  by  means 
of  a  special  pipe-line,  be  conducted  to  the  clearing  basins, 
arranged  in  the  soda  cell  stuff  plant. 

Sixth — The  number  of  basins  to  be  put  up  for  purification 
and  clearing  of  the  washed  spent  leaches  is  set  down  at 
three,  with  a  cubic  contents  of  60  cubic  meters  each  and  a 
bottom  face  of  about  309  square  meters.  They  have  to  be 
put  up  in  such  manner  that  side  walls  and  bottom,  in  pro- 
portion to  the  pressure  of  the  liquid,  are  sufficiently  strong 
and  made  watertight,  laid  with  cement  mortar,  and  besides 
are  lined  inside  with  a  layer  of  cement  to  obtain  perfect 
impenetrableness. 

Seventh — The  precipitates  obtained  in  the  purification  of 
the  waste-waters,  according  to  Dr.  Frank's  method,  if  not 
utilized  as  fertilizers,  must  after  drying  in  the  air  again  be 
burned. 

Eighth — The  letting  off  of  the  waste-water  from  the  clari- 
fying basin  must  be  regulated  in  such  manner  that  not  more 
than  1.5  liter  per  second  are  admitted  to  the  Aschaff. 

Ninth — The  circular  saws  employed  in  the  plant,  and  ail 
parts  of  the  transmission,  as  gearing,  pulleys,  etc.,  as  far  as 
in  the  reach  of  the  workmen,  must  be  provided  with  suffi- 
cient means  of  protection. 

PLANNING  OF  CELLULOSE  FACTO  RIES. 

From  a  consideration  of  the  different  processes  of  cellulose 
manufacture  as  treated  in  the  previous  chapters  and  consid- 
ering the  difficulties  and  aggravations  by  adjacent  property- 
holders  and  the  authorities,  it  will  be  plain  that  when  newly 


216  THE    MANUFACTURE    OF    CELLULOSE. 

planning  a  cellulose  factory  the  utmost  importance  must  be 
paid  to  the  right  selection  of  the  place.  As  in  cellulose 
manufacturing  there  is  not  a  large  consumption  of  power, 
and  the  steam  engines  to-day  are  built  so  that  the  consump- 
tion of  coal  is  reduced  to  a  minimum,  it  is  not  necessary  to 
look  for  cheap  water-power,  but  rather  for  the  immediate 
neighborhood  of  a  large  river,  which  facilitates  the  direct 
supply  of  wood  or  part  of  it  by  water,  and  may  also  permit 
the  shipping  of  the  finished  product,  but  principally  facili-. 
tates  the  disposition  of  the  waste-waters. 

If  possible  the  lot  should  not  be  situated  above  a  city, 
and  not  too  near  a  large  community,  or  especially  valuable 
plantations,  or  parks.  When  the  supply  of  wood  is  not  pos- 
sible directly  by  the  river,  it  is  most  necessary  to  be  near 
a  railroad  and  to  possess  a  track  if  possible  right  into  the 
with  every  cellulose  factory.  In  the  rarest  cases,  a  factory 
will  be  so  situated  that  it  may  get  its  whole  supply  of  wood 
nearby,  i.  e.,  carting  it  directly  from  the  woods.  Almost 
always  the  factories  are  dependent  on  the  supply  from 
greater  distances,  and  it  is  well,  if  besides  the  high  railroad 
freights,  the  cost  of  carting  from  and  to  the  depot  has  not 
to  be  added.  It  must  be  considered  that  every  cellulose  fac- 
tory, for  instance,  figured  for  but  one  Mitscherlich  digester, 
for  a  yearly  production  of  9,000,000  liters  of  dry  cellulose, 
about  7,000  volumeters  of  wood  are  necessary,  which  at  its 
mean  amount  of  dryness,  alone  represents  a  weight  of 
3,680,000  kilometers.  When  considering  the  other  mate- 
rials necessary  for  the  above  amount  of  wood  per  year,  the 
following  statement  is  obtained: 

Kilo- 
Materials,  meters. 

Wood  (7,000  volumeters) 3,680,000 

Cellulose :  Dry,  900,000,  moist 1,800,000 

Pyrites 530,000 

Lime 180,000 

Coal    1,200,000 

Other  materials  .  110,000 


Total   7,500,000 

From  this  statement  it  will  be  seen  that  for  100  kg.  air- 
dry  cellulose  about  58  per  cent,  of  pyrites  are  used.  It  is  to 
be  remarked,  however,  that  factories  with  larger  plants  use 


THE    MANUFACTURE    OF    CELLULOSE.  217 

but  50  per  cent.,  or  only  45  per  cent,  of  pyrites,  according  to 
quality  and  other  circumstances.  When  employing  pure  sul- 
phur, which  is  better  in  many  instances,  the  consumption 
is  much  less.  Herrmann  Brungger,  according  to  his  experi- 
ences, states  the  consumption  of  99  per  cent,  of  sulphur,  as 
9.77  kg.  for  100  kg.  of  air-dry  cellstuff. 

Therefore,  for  every  single  digester  at  least  7,500,000  kilos 
of  material  have  to  be  carried  to  and  from  the  factory  each 
year,  which,  even  with  favorable  situation  of  the  factory, 
gives  a  high  expense  for  freight ;  especially  as  in  recent  years 
the  manufacturer  cannot  evade  the  request  of  the  customers 
to  deliver  the  cellulose  free.  Favorable  means  of  communica- 
tion must  therefore  also  be  considered  of  first  importance, 
when  selecting  the  place.  It  would  consequently  not  be 
economy  to  select  a  lot  perhaps  cheap  and  otherwise  suitable 
but  lying  off  the  roads. 

Another  important  condition  is  abundance  of  pure  water. 
If  the  purity  is  not  satisfactory,  or  at  times  turbulance  is 
caused  by  rain,  etc.,  there  from  the  very  beginning,  the  plan- 
ning of  large  clearing  ponds  or  other  arrangements  must  be 
cared  for.  Care  must  be  taken  that  the  clearing  arrangement 
or  wells  are  above  the  plant,  in  regard  to  the  direction  of  the 
river,  so  that  a  contamination  by  the  waste-waters  partially 
sinking  into  the  soil  is  excluded. 

When  the  lot  is  not  level  but  somewhat  hilly,  this  can  be 
used  with  advantage  by  putting  the  pyrite-ovens  and  the 
towers  so  high  that  the  leach  can  be  conducted  through  a 
pipe-line  directly  into  the  digesters  from  the  leach  tanks, 
whereby  a  leach  pump  becomes  unnecessary.  By  the  higher 
situation  of  the  towers  sulphurous  acid  escaping  on  top  enters 
the  high  layers  of  the  air  and  thus,  before  falling  down,  is 
more  diluted  and  made  harmless. 

It  would  not  be  of  much  value  to  go  here  beyond  the  general 
rules  for  planning  a  cellulose  factory,  and  perhaps  to  show  for 
example  in  sketch  one  or  several  existing  plants,  as  every 
new  plant  must  suit  the  local  conditions  and  also  the  instruc- 
tions of  the  local  authorities.  Besides,  in  every  plan  the  pro- 
jected size  of  the  planned  establishment  and  means  of  the 
proprietor  must  be  taken  into  consideration,  and  above  all 
the  system,  according  to  which  the  cellulose  is  to  be  made. 
To  execute  the  plan  of  a  new  establishment  in  every  single 
instance  a  technical  expert  must  certainly  assist. 

From  the  standpoint  of  the  paper  manufacturers  must 


218  THE    MANUFACTURE    OF    CELLULOSE. 

next  be  viewed  the  two  large  groups  of  the  soda  and  sulphite- 
cellulose,  which,  because  in  the  manufacture  of  paper,  they 
are  intended  to  take  the  place  of  the  rags,  partially  or  en- 
tirely, he  likes  in  general  to  compare  with  the  cotton  and 
linen  fibre  because,  at  least  in  its  qualities,  they  do  in  fact 
show  much  similarity  to  them.  Both  linen  and  cotton  fibres 
are  employed  with  equal  importance,  but  often  one  can  by 
no  means  be  substituted  for  the  other ;  where  very  particular 
qualities  of  a  paper  are  in  question.  As  a  rule,  however, 
the  greater  value  must  be  acknowledged  to  the  linen  fibre. 
The  same  with  the  two  celluloses  mentioned :  the  soda  cellu- 
lose is  generally  softer,  more  similar  to  cotton,  finding  em- 
ployment for  many  purposes,  however  the  sulphite-cellulose 
has,  in  a  measure,  displaced  it  because  it  is  unconditionally 
firmer,  some  sorts  can  be  bleached  better  and  besides  it  is  on 
the  average  sold  somewhat  cheaper. 

The  cause  of  the  difference  not  only  of  the  two  principal 
groups,  but  also  of  the  celluloses  of  the  different  sulphite 
processes  compared  with  each  other,  can  be  perceived  from  the 
comparison  on  the  next  page,  which,  while  not  quite  com- 
plete, shows  however,  that  the  pressure  and  the  temperature 
at  which  the  fibre  has  been  boiled,  is  of  great  influence. 

From  this  can  be  learned  that  especially  the  soda-cellulose 
is  produced  with  very  high  pressure,  high  temperature,  but  in 
proportion  short  duration  of  boiling;  that  the  sulphite-cellu- 
loses are,  on  the  average,  worked  with  low  pressure,  low  tem- 
perature and  shorter  time  of  boiling,  and  that  especially  in 
the  manufacture  of  Mitscherlich  cellulose  the  lowest  tem- 
perature, the  lowest  pressure,  but  the  longest  time  for  boiling 
are  employed.  According  to  the  last-mentioned  method  boiling 
is  consequently  the  most  carefully  done,  i.  e.,  it  is  evident  that 
in  slowly  removing  the  incrusting  constituents,  employing 
but  the  most  necessary  degrees  of  heat,  the  proper  fibre  must 
be  spared  most,  the  produced  cellulose  must  consequently 
possess  the  greatest  firmness,  And  such  is  indeed  the  case. 

The  author,  when  a  paper  manufacturer,  had  for  a  long 
time  worked  in  most  of  the  different  sorts  of  cellulose  and  re- 
ceived his  supply  of  Mitscherlich  cellulose  from  different  fac- 
tories; but  in  regard  to  firmness  this  product  has  not  yet 
been  surpassed  by  any  other  system. 

When  comparing  soda-cellulose  with  the  cotton  fibre,  the 
Mitscherlich  cellulose  must  be  put  in  place  of  the  toughest 
linen  and  hemp  fibre  and  accordingly  the  other  principal  sul- 


THE    MANUFACTURE    OF    CELLULOSE. 


219 


g 

13 

co 

o 

«-. 

CL 

P 

Trancke 
Ritter-Kell 
Mitscherlic 

s  «  $  5  a 

n.    cr    cu    3     o> 

3      rr  H"      p      ""^ 

f  II  3  » 

s                    dd 

a  a  > 

3       P       3 

°s  -  « 

(T                   ^ 

n>           PT 

^     .      P 

2 

1 

O 

P" 

1 

Cn 

Highest  pressure  of 

•£"    9s* 

Co     Cn     Cn 

-P>     4i-              Cn 

O^       '        O^ 

00      O       00 

steam  in  atmos- 
phere. 

m 

« 

M 

» 

o 

i 

o 

1 

Highest  temperature 

8 

0 

5 

o 

10 

o 

in  degrees  Celsius. 

Cn      C\     W 

10       ""*       CO 

Co 

Duration  of  boiling 

Co     Co      »H 

00      <3\     ^3 

HH      KN,    vO       O 

4^ 

O 

in  hours. 

Cn 

Cn      ON 

o 

"o          ^ 

O         O      t-i 
i           *          KJ 

IT 

•O\         t-H              Q 

o 

w 

03           P 

w  1  w 

0 

BC 

w 

220  THE    MANUFACTURE    OF    CELLULOSE. 

phite  processes,  Ritter-Kellner,  Graham  and  Fladquist  would 
represent  the  finer  fibres  of  linen.  The  comparison  is  also  fit- 
ting in  reality,  because  it  cannot  be  denied  that  the  Mitscher- 
lich  cellulose,  with  all  its  advantages,  has  however  the  dis- 
advantages, to  be  somewhat  less  pure,  for  which  reason,  when 
bleached,  it  cannot  well  be  employed  for  the  finer  sorts  of 
paper,  while  the  cellulose  according  to  Ritter-Kellner  and  a 
few  other  related  processes  great  firmness  is  combined  with 
great  purity,  and  in  the  first  qualities  by  glaring  whiteness, 
so  that  it  can  be  used  with  advantage  for  the  best  papers. 
Lately  Mitscherlich  cellulose  is  also  produced  bleached  very 
white  and  faultlessly  pure. 

(The  End.) 


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